R-3 Repository :: Browsing by Author "Curl, Robert F., Jr."

Browsing by Author "Curl, Robert F., Jr."

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Assignment of microwave rotational spectra by computer
(1968) Thomas, Dorothy Jean; Curl, Robert F., Jr.
A computer program was written to assign the rotational quantum number transitions to the lines in a microwave spectrum. Lines in the spectrum of allyl alcohol were assigned using this program.
Color center laser kinetic spectroscopy
(1989) Stephens, James Wesley; Curl, Robert F., Jr.
High resolution color center laser kinetic spectroscopy has been used to study the kinetics and spectroscopy of free radicals. The radicals are produced in a flowing system by the excimer laser photolysis of stable precursors. The transient infrared absorptions of the radicals are monitored with better than 1 $\mu$s time resolution. Spectra of the ethynyl radical (C$\sb2$H), produced by photolysis of acetylene, were collected between 3000 and 3600 cm$\sp{-1}$ with a goal of identifying the CH stretching fundamental of the molecule. A number of new bands of C$\sb2$H and its carbon-13 analogue ($\sp{13}$C$\sp{13}$CH) were observed and rotationally analyzed. These bands include three C$\sb2$H bands of $\sp2\Sigma\sp+$ + $\gets$ $\sp2\Sigma\sp+$ symmetry, one C$\sb2$H band of $\sp2\Pi$ $\gets$ $\sp2\Pi$ symmetry, three $\sp{13}$C$\sb2$H bands of $\sp2\Sigma\sp+$ + $\gets$ $\sp2\Sigma\sp+$ symmetry, and one $\sp{13}$C$\sb2$H band of $\sp2\Pi$ $\gets$ $\sp2\Pi$ symmetry. A number of $\sp{13}$C analogues of $\sp{12}$C$\sb2$H bands were identified. However, no conclusive assignment has been made for the CH stretch. Two tentative assignment schemes are given for several of the bands. The kinetics of the C$\sb2$H + O$\sb2$ reaction were studied with a goal of determining the reaction products. OH radicals were determined to be a minor product of this reaction. Experiments designed to determine the relative importance of the hydrogen atom producing channel were inconclusive. In other kinetic studies, a high temperature furnace was constructed to determine the temperature dependences of the product channels of the NH$\sb2$ + NO reaction. The reaction was initiated by the photolysis of NH$\sb3$ in the presence of NO. The branching ratios of the OH and H$\sb2$O producing channels were determined at 26, 400, 700, and 925$\sp\circ$C by comparison of the increase in OH and H$\sb2$O absorption signals with the decrease in an NH$\sb3$ absorption signal. Branching ratios were calculated from the raw signals by using the infrared cross sections of the molecules, measured in separate experiments. The branching ratio of the OH channel is 14% at room temperature and increases to 25% at 925$\sp\circ$C. The total of the two channels (OH plus H$\sb2$O) accounts for 100% of the reaction at room temperature; however, this number drops to about 80% for higher temperatures, possibly indicating the onset of another channel.
Color center laser kinetic spectroscopy: Evidence for quasilinearity of HCCN
(1994) Farhat, Shahla Khan; Curl, Robert F., Jr.
The C-H stretching fundamental of the free radical HCCN has been investigated under high resolution using infrared kinetic spectroscopy. This transient molecule was produced by the flash photolysis of dibromoacetonitrile (Br$\sb2$HCCN) at 193 nm and its transient infrared absorption spectrum probed using a color center laser. Spectra of the molecule were collected between 3182 and 3274 cm$\sp{-1}$. The rotational analysis of the $\nu\sb1$ fundamental places its origin at 3246.657 cm$\sp{-1}$. Four hot bands associated with the bending vibrations have been observed; the vibrational and rotational assignment of three of these bands $\nu\sb1 + \nu\sb5 - \nu\sb5$, $\nu\sb1 + \nu\sb4 - \nu\sb4$, and $\nu\sb1 + 2\nu\sb5\sp{\pm 2} - 2\nu\sb5\sp{\pm 2}$ is definite. The $\nu\sb5$ energy was obtained by measuring the intensity of a line of the $\nu\sb1 + \nu\sb5 - \nu\sb5$ band relative to one of the fundamental and calculating the energy assuming a room temperature Boltzmann distribution. A comparison of this energy with that of quasilinear fulminic acid, HCNO, and with theoretical calculations suggests a similar floppy HCX bending potential.
Difference frequency generation: Spectrometers and spectroscopy
(1997) Eckhoff, Wade Charles; Curl, Robert F., Jr.
The theory of difference frequency generation has been further developed. Derived from basic principles, the equations developed here accurately predict the conversion of power to the idler wave. Critical phasematching can now be modeled with ellipticity in both beams and the effects of double refraction and non-normal incidence upon the crystal treated. It is no longer necessary to focus the beams into the center of the crystal nor is it necessary to have an equal confocal parameter in the two drive beams. A mid-infrared spectrometer based on titanium:sapphire pumped difference frequency generation in silver thiogallate (AgGaS$\sb2$) has been constructed in order to conduct high resolution spectroscopy on free radicals. Detector limited sensitivity has been demonstrated with an estimated source bandwidth of 0.00003 cm$\sp{-1}$. The process used to calibrate scans has been improved and calibration accuracy of 0.001 cm$\sp{-1}$ is now routine. With the silver thiogallate spectrometer, the infrared spectrum of the monodeuterated propargyl radical (CH$\sb2$CCD) has been acquired. Approximately 250 lines have been positively identified and assigned to the $\nu\sb1$ C-D stretch in the region between 2300 cm$\sp{-1}$ and 2400 cm$\sp{-1}$. The spectrum consists of a-type transitions ($\Delta$K$\sb{\rm a}$ = 0) with a fully resolved K subband structure, in contrast to the CH stretch of the normal radical. This resolved structure is due to a P$\sb{\rm a}$-type Coriolis interaction or a Fermi resonance in the molecule. These interactions may be responsible for the fact that we were unable to identify the odd K subbands, though positive identification of the K$\sb{\rm a}$ = 0, 2, 4, and 6 subbands was made and used to determine rotational constants for the radical. A spectrometer based on difference frequency generation in gallium selenide (GaSe) was constructed. Precise phasematching characteristics were determined as well as the potential power produced in the process. The instrument is continuously tunable in the 8.8-15.0 $\mu$m wavelength region.
Diode laser kinetic spectroscopy
(1991) Unfried, Kenneth Gary; Curl, Robert F., Jr.
High resolution infrared diode laser kinetic spectroscopy has been used to study reaction kinetics and spectroscopy of short-lived species. These unstable molecules were produced in a flowing system by excimer laser photolysis of suitable precursors. Their concentrations were monitored using an infrared diode laser with fast InSb detectors. Time resolution of better than 1$\mu$s was achieved. HNO production is predicted by the reaction sequence NH$\sb2$ + NO $\to$ HN$\sb2$ + OH, HN$\sb2$ + NO $\to$ HNO + N$\sb2$ in the Miller mechanism for the thermal deNOx process. A search was made for the HNO molecule in the reaction system NH$\sb2$ + NO at room temperature using diode laser infrared kinetic spectroscopy to search for NH stretch absorptions of HNO. No HNO attributable to the deNOx process was observed. Sensitivity calibration measurements using known amounts of HNO produced from the reaction of HCO with NO were used to set an upper bound of 1% for the conversion of NH$\sb2$ into HNO. The high resolution infrared spectrum of the heavy atom antisymmetric stretch of the ketenyl radical (HCCO) was observed by means of infrared kinetic spectroscopy. Ketenyl was produced by 193 nm photolysis of ketene. The resulting transient absorption was probed with an infrared diode laser. Individual rovibrational transitions have been identified and molecular parameters have been determined from a least-squares fit of the data. The band origin is located near 2023 cm$\sp{-1}$. Acquisition of ketenyl infrared spectra allowed for determination of reaction rate constants by directly observing ketenyl decay. Kinetic studies of the ketenyl radical's reaction with nitric oxide, oxygen, acetylene and ethylene were conducted. A second order rate constant of 4.4(10) $\times$ 10$\sp{-11}$ cm$\sp3$molecule$\sp{-1}$s$\sp{-1}$ was obtained for the reaction with NO and a second order constant of 6.5 $\times$ 10$\sp{-13}$ cm$\sp3$molecule$\sp{-1}$s$\sp{-1}$ was obtained for the reaction with O$\sb2$. Acetylene appeared not to react with the ketenyl radical. An upper limit of 3.8 $\times$ 10$\sp{-13}$ cm$\sp3$molecule$\sp{-1}$s$\sp{-1}$ for the rate constant was determined by measuring the ketenyl decay in the presence of acetylene. The addition of ethylene appeared to slow the ketenyl decay. This behavior was attributed to the reaction of ethylene with a chemical species (probably H atoms) responsible for depletion of ketenyl.
Diode laser kinetic spectroscopy of formyl
(1988) Dane, Clifford Brent; Curl, Robert F., Jr.
A tunable diode laser infrared high-resolution spectrometer was constructed to study the spectroscopy and kinetics of free radicals. A method for producing diode laser frequency scans which are several wavelengths long, linear in frequency, and readily and accurately calibrated from reference spectra has been devised. The laser is current scanned under computer control over short overlapping segments between each of which a temperature step is made. Each segment is then linearized and pieced together to provide a final spectral scan. High-resolution spectra of transient species were collected using either magnetic rotation spectroscopy or flash kinetic spectroscopy. The high-resolution infrared spectrum of the CH stretching fundamental of the formyl radical (HCO) was observed by means of infrared kinetic spectroscopy using 308 nm (XeCl) excimer laser flash photolysis of formaldehyde or acetaldehyde followed by diode or difference-frequency laser probing of the transient absorption. The spectra obtained were assigned and fitted with rotational, spin-rotational, and centrifugal distortion constants resulting in a v$\sb1$ band origin of 2434.48 cm$\sp{-1}$. New ground state constant are reported from a least-squares fit combining the v$\sb1$ infrared data with previous microwave and far-infrared laser magnetic resonance (FIR LMR) measurements. Fixed-frequency studies of infrared absorptions using the spectrometer allow the time-resolved investigation of chemical dynamics on submicrosecond time scales. A method of locking the diode laser output frequency to an external vacuum-spaced etalon by modulating the optical pathlength of the etalon was investigated. Using this technique, the rate constant of the reaction of HCO with O$\sb2$ was measured.
High-resolution infrared spectroscopic study of the non-rigid radicals HCCN and DCCN
(2001) Hung, Pui Yee; Curl, Robert F., Jr.
This thesis is divided into two sections. The first section focuses on the IR spectroscopic determination of the CD/CH vibrational energy spacings of the quasilinear HCCN and DCCN nu5 bending mode. We have developed an in-house program to analyze and assign the HCCN and DCCN spectra. The program has three functions, namely, spectral contour simulation, P and R transition strength calculation, and diagnostic least squares fitting. The spectral contour simulation was the most valuable tool. It generated the Q contours of transitions between various states for comparison with the observed spectra. Overall, we have successfully assigned the HCCN and DCCN nu1+2nu 5+/-2←nu5+/-1, nu 1+3nu5+/-3←2nu5 +/-2 combination bands and the HCCN nu1+3nu 5+/-3←3nu5+/-3 hot band. Using this assignment with the previous published hot band analysis, 18,19 we determined the HCCN 2nu5+/-2←nu 5+/-1, 3nu5+/-3←2nu 5+/-2 and DCCN 2nu5+/-2 ←nu5+/-1 vibrational energy gaps to be 212.821, 272.864 and 133.106 cm-1, respectively. The second part of the thesis focuses on the design and development of a supersonic jet cooling system. This system aims to expand our high-resolution IR spectroscopic work to cover much larger and more non-rigid species. A similar attempt was made a decade ago; however, the prototype was not sufficiently reliable to pass the testing stage. This project expands on our previous effort and focuses on designing a more reliable and better-performing system. We replaced the home-made pulsed valve with a more reliable commercial valve and greatly reduced the maintenance time and enhanced the ease of operation. To increase the efficiency of radical generation, we adopted the novel slit discharge method25 in place of the photolysis approach. Finally, we used a more compact and stable Herriott multipass cell design to overcome the signal broadening and averaging effects introduced by the previous White-type multipass cell. Overall, we have made much progress in enhancing the stability and performance of the system.
High-resolution spectroscopy of propargyl radical
(1998) Yuan, Li; Curl, Robert F., Jr.
The high resolution infrared spectrum of the $\nu\sb1$ acetylenic CH stretch of the propargyl radical H$\sb2$CC$\equiv$CH has been obtained by the color center laser kinetic spectroscopy method. The propargyl radical is produced by flash photolyzing stable precursors propargyl bromide or propargyl chloride using the ArF excimer laser. The transient infrared absorptions of the propargyl radical are probed by the color center laser. More than 300 absorption lines were observed in the frequency region of 3304 cm$\sp{-1}$ to 3337.5 cm$\sp{-1}.$ Most of these lines were assigned to the different K subbands of the $\nu\sb1$ fundamental vibrational mode except those lines belonging to an unknown hot band. The upper state energies were obtained by adding the ground state energies appropriately to each observed P and R transitions. Then these upper state energies were fitted by a least squares fitting program and the upper state rotational constants A, B, C and centrifugal distortion constants $\rm\Delta\sb{K},\ \Delta\sb{NK}$ and $\rm\Delta\sb{N}$ together with the band origin $\nu\sb1$ were obtained from the fitting. K = 2$\pm$ sublevels were found perturbed by another vibrational mode so they were not used in the fitting. The nature of this perturbation was recognized as a Coriolis interaction.
Investigation of ethynyl radical kinetics using infrared diode laser kinetic spectroscopy
(1990) Lander, Deborah Rosemary; Curl, Robert F., Jr.
High resolution infrared diode laser kinetic spectroscopy has been used to investigate the properties of C$\sb2$H reaction kinetics. The ethynyl radical (C$\sb2$H) was produced in a flowing system by excimer laser photolysis (ArF, 193 nm) of either CF$\sb3$CCH or C$\sb2$H$\sb2$ and the transient infrared absorptions of C$\sb2$H or possible reaction products were followed with the diode laser probe. The kinetics of the C$\sb2$H + O$\sb2$ reaction were studied with a goal of determining the reaction products. Only two reaction products were observed, CO and CO$\sb2$, with the amount of CO produced being about five times larger than the amount of CO$\sb2$ produced. Both products are produced in vibrationally excited states. CO$\sb2$ was produced long after C$\sb2$H reacted and thus is not a product of the direct reaction. Two processes leading to CO formation have been observed: a fast, direct process for which the rate of CO appearance approximately matches the rate of C$\sb2$H decay and a much slower indirect process. The fast process produces vibrationally excited CO (v = 5 $\gets$ 4 and higher). The indirect process is observed to be dominant for the lower vibrational transitions and its rate exhibits saturation with increasing O$\sb2$ pressure. In order to approximate these kinetics, it appears that at least two intermediates between C$\sb2$H and CO must be involved for the indirect process. In other kinetic studies, the rate constants of C$\sb2$H reactions were measured to see if other C$\sb2$H reactions might exhibit addition channels. The time decay of a C$\sb2$H infrared absorption line originating from the ground vibronic state was monitored as a function of reactant pressure to determine a second order rate constant. When possible the dependence of the reaction rate on helium pressure was investigated over the range of 8-70 Torr. Second order rate constants of 3.0(2) $\times$ 10$\sp{-12}$, 1.3(3) $\times$ 10$\sp{-10}$, 3.6(2) $\times$ 10$\sp{-11}$, 4.4(4) $\times$ 10$\sp{-13}$, 2.3(3) $\times$ 10$\sp{-13}$ cm$\sp3$ molecule$\sp{-1}$ s$\sp{-1}$ were obtained for the reactions of C$\sb2$H with CH$\sb4$, C$\sb2$H$\sb4$, C$\sb2$H$\sb6$, H$\sb2$ and D$\sb2$ respectively. A third order rate constant of 2.1(3) $\times$ 10$\sp{-30}$ cm$\sp6$ molecule$\sp{-2}$ s$\sp{-1}$ was obtained for the reaction of C$\sb2$H with CO.
Jet-cooled radical spectroscopy using a color center laser
(1990) Richnow, Marilyn Lea; Curl, Robert F., Jr.
Jet-cooled radical spectroscopy has been developed for its potential application to high resolution infrared spectroscopic studies of large radicals. In general, radicals containing more than three atoms heavier than hydrogen can not be studied in a room temperature cell using high resolution techniques. For such large species, the infrared spectrum becomes congested and unresolvably complex because of the presence of overlapping rotational lines and vibrational hot bands. By cooling radicals in a supersonic expansion, excited rotational and vibrational levels are depopulated, giving simplified spectrum. In this technique, radicals are produced inside a slit supersonic nozzle by 193 or 248 nm excimer laser photolysis of a gas mixture consisting of 1% suitable precursor seeded into 1-11 atm carrier gas (typically helium). To reduce the vibrational temperature of the hot radicals produced upon photolysis, the radicals are thermalized by collisions with the room temperature helium inside the slit thermalization region before expansion. The radicals are then cooled rotationally in the subsequent expansion, and their transient absorption is probed downstream of the slit orifice by a tunable, computer-controlled color center laser. The jet-cooled infrared spectroscopy technique was first tested on small radicals with known high resolution spectra. Small radicals such as NH$\sb2$, OH, and CH$\sb3$ have been observed in the jet with excellent sensitivity and low rotational temperatures. Rotational temperatures ranging from 13-25K and signal-to-noise ratios of 30-150 have been obtained for these radicals. Additionally, rotational temperatures of 10K have been observed for trans-nitrous acid, a stable species produced upon photolysis of nitric acid in the jet. Jet-cooled infrared spectroscopic studies of larger radicals were initiated since the technique proved successful in the production, cooling, and detection of small radicals. Spectroscopic searches were made for CH$\sb2$OH, t-HOCO, CH$\sb3$NH, C$\sb2$H$\sb3$, C$\sb3$H$\sb5$, and OH-Ar (radical van der Waals complex). Although no new radical species were conclusively observed in the jet photolysis experiments, the initial results of searches for these radicals, including the observation of several stable molecules produced upon photolysis of various precursors, have been described.
Laser microspectrofluorometry for the diagnosis of atherosclerosis
(1997) Fink, Tami Neal; Curl, Robert F., Jr.
Cardiovascular disease is a major cause of death in the U.S., and atherosclerosis, the principle cause of myocardial and cerebral infarctions, accounts for most of these deaths. In current clinical practice, cholesterol status, or atherosclerotic risk, is evaluated by fasting serum lipoprotein measurements. However, disease variation lies in the biologic responses of circulating blood cells and cells in the arterial wall, in the presence of given levels of plasma cholesterol. Lipid-laden monocytes or circulating macrophage 'foam cells' may be useful markers of atherosclerotic disease. Macrophage 'foam cells' can be identified by their massive accumulation of an atherogenic lipoprotein, oxidatively modified low-density lipoprotein (LDL). Oxidized LDL possesses unique fluorescence spectral characteristics that distinguish it from native (non-oxidized) LDL. Thus, fluorescence spectroscopy was chosen as a tool for identifying oxidized LDL accumulations in monocyte/macrophages, and may be useful for identifying a novel risk factor in the assessment of atherosclerosis. In cell suspension autofluorescence analysis, spectral characteristics of oxidized LDL were shown in cultured macrophages incubated with oxidized LDL preparations. Additionally, it was demonstrated that isolated peripheral blood monocytes may acquire spectroscopic signatures characteristic of oxidatively modified LDL. Identifying the percentage of oxidized LDL filled monocytes in a patient will be important in determining any correlation with atherosclerosis incidence or risk of atherosclerotic complications. Thus, more sophisticated analysis of the distribution of intracellular oxidized LDL content within a population of monocyte/macrophages required the development of instrumentation for spectroscopy at the microscopic level. A microspectrofluorometer was designed and constructed to detect intracellular oxidized LDL concentrations, based on autofluorescence signals, in individual cells smeared onto microscope slides. Good characterization of system losses improved the capability to quantify measurements in terms of absolute concentrations, a problem inherent in most fluorescence instruments. Using autofluorescence microspectrofluorometry, intracellular oxidized LDL concentrations could be identified within individual monocyte/macrophages incubated with oxidized LDL and calibrated with respect to oxidized LDL standards. Histologic comparisons using oil red O staining and transmission electron microscopy verified cultured macrophages were accumulating oxidized LDL. Increases in lipid droplets, cholesterol clefts, and secondary lysosomes correlated with increasing autofluorescence signals.
Overhauser effect and NMR spectra of n-methyl methylenimine
(1966) Chang, Chen-Fee; Curl, Robert F., Jr.
Pure liquid samples of the simple but rather reactive species N-Methyl Methylenimine were studied at -60°C. The conventional NMR spectra and double resonance spectra were taken. The NMR constants and relative signs of three spin-spin coupling constants were determined. Absolute signs of the coupling constants were discussed.
Photofragmentation studies of semiconductor positive cluster ions
(1989) Zhang, Qingling; Curl, Robert F., Jr.
Laser photofragmentation of Si, Ge, and GaAs positive cluster ions prepared by laser vaporization and supersonic beam expansion has been investigated in a tandem time-of-flight mass spectrometer. Si$\sb{\rm n}\sp +$ up to size 80, Ge$\sb{\rm n}\sp +$ and Ga$\sb{\rm x}$As$\sb{\rm y}\sp +$ up to a total of 31 atoms have been studied. Ga$\sb{\rm x}$As$\sb{\rm y}\sp +$ fragment in a nearly uniform pattern probably via a step-loss of atoms pattern with odd fragments being more prominent than their even neighbors. Both Si$\sb{\rm n}\sp +$ and Ge$\sb{\rm n}\sp +$ of all sizes show as one fragmentation channel loss of one atom to produce Si$\sb{n-1}\sp +$ or Ge$\sb{n-1}\sp +$. In addition, Si$\sb{\rm n}\sp +$ and Ge$\sb{\rm n}\sp +$ in the size range n = 10-30 photofragment to produce positive ions of about one half the mass of the parent. For Ge$\sb{\rm n}\sp +$ as n becomes greater than 30, this fragmentation becomes a pattern in which positive ions containing 10 (or 7) fewer atoms are the principal products at low laser fluence. Increased fluence seems to fragment these daughters in the same way as they would behave as primary ions. The Si$\sb{\rm n}\sp +$ ions of greater than 30 atoms do not show this 10 or 7 atom neutral loss. Both Si$\sb{\rm n}\sp +$ and Ge$\sb{\rm n}\sp +$ for n $>$ 30 show an additional channel in which small positive ion fragments in the n = 6 to 11 size range are produced. This channel requires high fluence and is shown to involve at least two 6.4 eV (ArF) photons for Si$\sb{60}\sp +$. The absence of intermediate fragments in this channel suggests that these large cluster ions break down into several clusters because the positive charge would be expected to stay with the larger fragment in a fission into two clusters as the ionization potentials of the neutral clusters decrease with size. A reflectron tandem time-of-flight mass spectrometer has been designed and constructed. The resultant high resolution makes the apparatus a highly efficient instrument for fragmentation and spectroscopic studies.
Spectroscopy of transition region species
(1988) Ulvick, Sydney James; Curl, Robert F., Jr.
Emission at the Na D lines has previously been observed from the intersection of crossed effusive beams of K and NaCl irradiated by a dye laser at wavelengths form 590nm to 735nm. The three beam signal is attributed to direct photoexcitation of KClNa transition region species. Further interpretation of these experiments is hampered, however, by broad translational and internal energy distributions of reacting partners. Supersonic beams of K and NaCl, both seeded in argon, were developed in order to reduce the distribution of translational and internal energies. It was hoped that insight into the reaction dynamics of the K+NaCl system would be revealed by the difference in collision energy between crossed effusive beams and crossed seeded beams. In addition, the rotational broadening of the K$\sb2$B$\sp1\Pi\sb{\rm u}$-X$\sp1\Sigma\sb{\rm g}\sp{+}$ spectrum collapses on cooling and therefore "artifact-clean" frequencies could be probed by the laser. Extensive characterization studies of the seeded beam sources were carried out. Mean velocities of K and NaCl were measured to be 1.3 $\times$ 10$\sp5$ and 1.1 $\times$ 10$\sp5$ cm/sec, respectively. Measurements of the rotational and vibrational energy distributions of K$\sb2$ present in the potassium beam reveal a rotational temperature of 12 $\pm$ 1$\sp\circ$K and vibrational temperature of 77 $\pm$ 13$\sp\circ$K. Time of flight experiments demonstrate a translational temperature for NaCl and K beams of 170$\sp\circ$K and 12$\sp\circ$K, respectively. Significant three beam emission at the 589.0nm Na D line is observed at the intersection of crossed seeded reagent beams of K and NaCl irradiated by a dye laser from 610nm to 750nm. This three beam signal is comparable to that previously observed with effusive sources. However, contrary to expectations the photoluminescence of the K beam at 589.0nm when laser excited in the region 610-750nm was much larger than for an effusive source. The seeded source potassium photoluminescence at 589.0nm is an order of magnitude larger than the seeded source three beam signal. In contrast, the three beam signal with an effusive K beam is substantially the largest signal in that system. Nevertheless, the narrow energy distribution of these supersonic sources and their ability to change the collision energy makes them very useful for further probing of the KClNa transition region species.
Statistical thermodynamics of one dimensional two component harmonic lattices
(1962) McNeil, Michael B. (Michael Brewer), 1938-; Curl, Robert F., Jr.; Kilpatrick, John E.; Brotzen, Franz R.
The microwave spectrum of quinuclidine
(1959) Johnson, Lauren G; Curl, Robert F., Jr.
The use of infrared kinetic spectroscopy to study small free radicals
(1998) DeSain, John Dennis; Curl, Robert F., Jr.
The technique of infrared kinetic spectroscopy has been used to study the reaction of the propargyl radical (C3H3) with nitric oxide (NO). The overall rate constant at the high pressure limit for the reaction was determined to be 1.09 +/- .28 * 10-11 cc molec-1 s -1 at 296 K. The reaction has an apparent negative activation energy for temperatures between 195--473 K and its rate constant is pressure dependent at 195 K and 296 K. At these temperatures the mechanism is believed to involve adduct formation. The establishment of an adduct equilibrium is not observed at higher temperatures, however. Instead the reaction is thought to form final stable products. A search was carried out for several possible reaction products including HCN, HCCN, HCNO, HCCH, HNC and H2CN. Several of these species were observed and their yields determined. These species were at most produced in 5% yield and are therefore not a major product channel. An alternative sources of these species are reactions between NO and other photolysis products. A possible explanation for the failure to observe any smaller molecular products is that the adduct does not dissociate at high temperatures and instead, rearranges to a stable isomer of C3H 3NO. Transient IR laser spectroscopy near 3100 cm-1 was used to observe the nu1 and nu13 transitions of the allyl radical, with their band origins found to lie at 3113.9779(3) cm -1 and near 3110.5 cm-1, respectively. Detailed assignment and analysis of the nu1 transition identified over 1100 transitions, and yielded improved values for DeltaK and phiK ground state centrifugal distortion constants, as well as a new set of excited state (nu1 = 1) rotational and centrifugal distortion constants, in addition to determining the band origin. Transitions involving states with quantum number up to Ka = 11 and N = 27 were identified. Strong perturbations were found in the excited state, included global perturbations of the Ka' = 3 branch, extensive perturbations in the Ka' = 2 and 4 branches, and very localized perturbations in the Ka' = 6 branch. The K a' = 9 and 10 branches appear to be the most perturbed. Possible sources for these perturbations are discussed.
Transition region spectroscopy of dialkali halides: Sodium(2)chloride and sodium(2) + atomic fluorine going to sodium fluoride + sodium
(1990) Spence, James Hunter; Curl, Robert F., Jr.
Molecular beam chemiluminescence from Na$\sb2$ + F $\to$ NaF + Na$\sp\*$ was dispersed and measured with a fast spectrograph. Attention was given to emission wavelengths at and around 388.5 and 342.8 nm, which correspond to the electric dipole forbidden atomic transitions Na 4s $\to$ 3s and 3d $\to$ 3s, respectively. It was hoped that the nascent products NaF and Na$\sp\*$ would interact such that these normally dis-allowed transitions could be observed, thereby constituting a direct glimpse of the three atom system late in the reaction event. A small emission peak was observed at the 3d $\to$ 3s transition wavelength, but its weak intensity could be explained by electric quadrupole radiation of the free atom rather than a reaction-induced breaking of dipole selection rules. No structured emission was observed at the 4s $\to$ 3s wavelength, although interference from Na$\sb2\sp\*$ may be obscuring an otherwise observable peak. In a second experiment, two lines of an argon ion laser are crossed with a single Na/NaCl beam in an effort to observe resolved laser-induced fluorescence of the stable molecule Na$\sb2$Cl. The copious emission from Na$\sb2\sp\*$ precluded any definitive identification of fluorescence from the target molecule. Finally, a detailed description is given of the f/2 spectrograph that was developed in this laboratory. The instrument observes a 100 nm wavelength region simultaneously, images atomic lines to a full-width-half-maximum (fwhm) of 2 nm, has a photocathode quantum efficiency of 3.1% at 800 nm, and exhibits only 36 counts per second dark current.

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