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  • 1
    Electronic Resource
    Electronic Resource
    Laser-induced fluorescence spectroscopy of NCS in a free jet expansion (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 762-774 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser-induced fluorescence excitation spectra have been recorded for many vibronic transitions of the A(2Π)–X(2Π) and B(2Σ+)–X(2Π) systems of NCS under supersonic free jet expansion conditions. New assignments have been made for many of these bands and several of the assignments from previous work have been revised. Vibronic energies have been determined for levels involving excitation of all three vibrational modes in the ground electronic state and both excited electronic states. A detailed rotational and vibrational analysis has been carried out for levels involving excitations of the two stretching modes and the many rotational and potential function constants have been determined for the A and X states. The variation of the spin–orbit constant with vibrational level has also been investigated. Results of this paper provide the ground work for a detailed analysis of the Renner–Teller effect in the bending vibrational mode of this radical for both the X2(Π) and A(2Π) states to appear in a forthcoming paper. They also provide a spectroscopic database for future dynamical and kinetics studies of processes involving this radical.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457128
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  • 2
    Electronic Resource
    Electronic Resource
    Photodissociation of RNCS and RSCN (R=H, CH3, C2H5) : Evidence for an excited state isomerization and energy deposition in the NCS product (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2337-2345 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The 248 and 193 nm photodissociation of the series of molecules RNCS and RSCN (R=H, CH3, C2H5) has been investigated. Laser-induced fluorescence of the radical NCS was used to probe the energy deposition in the R+NCS channel of this dissociation, however excitation to many vibrational states of NCS caused spectral congestion which prohibited direct measurement of populations of individual levels. A single-photon dissociation channel leading to RS and CN was observed for both isomers of all of the precursor molecules. While this was expected for the thiocyanate species, no direct channel to these products is available for the isothiocyanates. This observation is discussed in terms of an excited state isomerization of these molecules. Measured ratios of CN to NCS production for all compounds provide additional support for this mechanism and suggest a significant barrier to the process. Comparison of nascent laser-induced fluorescence (LIF) spectra of NCS with spectra obtained following different amounts of collisional relaxation suggests that all three vibrational modes were equally excited with a vibrational temperature of roughly 4500 K. The rotational temperature was estimated to be less than 1000 K. A spin–orbit population inversion was observed for all vibrational levels with approximately 75% of the population in the upper spin–orbit component of the vibrationless and low lying bending excited levels. No simple model is found to explain the photodissociation dynamics or the isomerization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459013
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  • 3
    Electronic Resource
    Electronic Resource
    Photodissociation of RNCS and RSCN (R=H, CH3, C2H5) at 248 and 193 nm: CN product energy distributions (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2346-2356 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodissociation of the molecules RNCS and RSCN (R=H, CH3, and C2H5) was investigated at 248 and 193 nm and the internal energy distributions in the CN resulting from the RS+CN fragmentation channel were probed by laser induced fluorescence. These CN distributions were identical for formation from the isomer pairs in agreement with an excited state isomerization postulated earlier. At 248 nm, all precursors lead to nearly thermal CN rotational distributions with rotational temperatures of approximately 1100 K in v=0 and 800 K in v=1. The vibrational distributions could not be characterized by the same temperatures. At 193 nm, contributions from two apparently different dissociation channels were observed. The CN rotational populations showed a narrow, strongly peaked distribution lying on a broad, approximately statistical distribution. For HNCS, this peak occurs near N=10 suggesting dissociation from an excited state with a linear NCS skeleton. For the alkyl precursors, the peak occurs at very high rotational quantum number (N=70) indicating an excited state with a bent NCS framework. Vibrational distributions with population out to v=6 were observed. In all cases, the apparent statistical part of the rotational distribution and the vibrational distributions can be described by a prior function derived assuming that the internal modes of the alkyl substituent are not involved in any energy redistribution during the dissociation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459014
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  • 4
    Electronic Resource
    Electronic Resource
    Measurement of (00v3) levels in X 2Π NCO by stimulated emission pumping spectroscopy (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7218-7228 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser induced fluorescence measurements of NCO formed in the reaction CN+O2→NCO+O in a free jet expansion are reported. The rotational temperature achieved in the experiments was typically 10–15 K and absorption from vibrationally excited levels was very much reduced in intensity. Two bands in the A˜–X˜ system, the v1, v2, v3=200–000 and 120–000, of the radical were rotationally resolved for the first time, and wavelength resolved laser excited fluorescence measurements have been used to characterize many ground state vibronic energy levels below 6000 cm−1 in energy. Stimulated emission pumping experiments were carried out on vibronic levels associated with the ν3 vibration with 1≤v3≤3 in the electronic ground state. Harmonic and anharmonic constants were determined, together with the spin–orbit coupling parameters and rotational constants for these levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462426
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  • 5
    Electronic Resource
    Electronic Resource
    Stimulated Emission Pumping: Applications to Highly Vibrationally Excited Transient Molecules (1992)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physical Chemistry 43 (1992), S. 127-152 
    Details
    ISSN: 0066-426X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.pc.43.100192.001015
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  • 6
    Electronic Resource
    Electronic Resource
    Comment on "The ν1+ν3 combination mode of C3 in Ar and Kr matrices: Evidence for a bent structure'' [J. Chem. Phys. 99, 7371 (1993)] (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 5413-5413 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The weight of recent experimental and theoretical work on C3 shows that the isolated molecule is truly linear, i.e., the minimum of the bending potential is at the linear configuration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467329
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  • 7
    Electronic Resource
    Electronic Resource
    Initial vibrational level distribution of HCN[X˜ 1Σ+(v10v3)] from the CN(X 2Σ+)+H2→HCN+H reaction (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 4224-4236 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction of the cyano radical (CN) with hydrogen was studied by time-resolved infrared absorption spectroscopy of individual rovibrational states of HCN. The initial vibrational level distribution of HCN(v10v3) was determined by plotting the time dependence of the fractional population of a vibrational level and extrapolating these curves to the origin of time. The experiments were carried out at two temperatures, 293 and 324 K, with similar results. It was estimated that about 50% of the available reaction exothermicity was deposited as vibrational excitation of the HCN product. Surprisingly, the HCN(101) vibrational level received a significant fraction of the observed vibrational population, implying that the CN vibration was not really a spectator bond in the reaction dynamics. Furthermore, the observed HCN(v10v3) vibrations only account for about 27% of the initial HCN population produced in the title reaction. A significant fraction of the product HCN molecules must have been produced with the bending mode excited, likely in combination with the H–C stretch vibrations. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477028
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  • 8
    Electronic Resource
    Electronic Resource
    The initial vibrational level distribution and relaxation of HCN[X˜ 1Σ+(v1,0,v3)] in the CN(X 2Σ+)+CH4→HCN+CH3 reaction system (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 4533-4549 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction of the cyano radical (CN) with methane was studied by time-resolved infrared absorption spectroscopy by monitoring individual rovibrational states of the HCN and CH3 products. The initial vibrational level distribution of the bendless vibrational levels of HCN(v1,0,v3) was determined by plotting the time dependence of the fractional population of a vibrational level and extrapolating these curves to the origin of time. About 20% of the HCN products were observed to be initially produced in the HCN(v1,0,v3) vibrational levels, with v1 and v3=0,1,2. The CN radical was created by laser photolysis of three different precursors. Each photolyte provided a different initial vibrational level distribution of CN; however, similar initial HCN(v1,0,v3) vibrational level distributions were obtained independent of the CN radical precursor. This may indicate that the CN radical does not act as a spectator bond during the course of a reactive encounter for this system. The time dependence of the CH3 (00000) ground state was also followed using time-resolved infrared absorption spectroscopy. Preliminary data indicates that a large fraction, if not all, the CH3 radicals are produced in their ground state in the title reaction. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472537
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  • 9
    Electronic Resource
    Electronic Resource
    Study of Renner–Teller, spin–orbit, and Fermi-resonance interactions in X˜ 2Π (v1v20) levels of NCO by stimulated emission pumping spectroscopy (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 4583-4595 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report extensive measurements of rovibronic levels in the 020/100 and 040/120/200 Fermi-resonant polyads of NCO. The levels were accessed by the technique of stimulated emission pumping spectroscopy in a supersonic free jet expansion following excitation of bands in the A˜ 2Σ+−X˜ 2Π spectrum of the radical. The data were analyzed in terms of an effective Hamiltonian which explicitly included reference to all the possible vibronic levels of 2Π symmetry in the polyad under consideration. The effects of levels outside these were treated by perturbation theory. The model was successful in fitting the data close to the experimental measurement precision and the resulting parameters were interpreted in terms of the harmonic and anharmonic vibrational terms. The effective Renner–Teller coupling parameter in NCO varied with vibrational level; however, parameters describing the Fermi-resonance interaction were found to be constant for all the levels investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463861
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  • 10
    Electronic Resource
    Electronic Resource
    The initial vibrational state distribution of HCN X˜ 1Σ+(v1,0,v3) from the reaction CN(2Σ+)+C2H6→HCN+C2H5 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7966-7982 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction of the cyano radical (CN) with ethane was studied using time-resolved infrared absorption spectroscopy to monitor individual rovibrational states of the HCN product. A method is described that can be used to determine the initial vibrational state distribution at pressures of several Torr. This technique was applied to the title reaction to determine that the vibrational states of HCN(v1,0,v3), where v1, v3=0, 1, and 2, were not directly populated in the title reaction to any significant extent. The initial vibrational energy content of the CN radical was also varied but did not influence the initial population in the HCN vibrational levels probed in this experiment. The time dependence of HCN(v1,0,v3) was followed and interpreted in terms of bimolecular rate constants for vibrational relaxation with ethane. The title reaction is mode specific in its energy disposal in that at least every HCN product appears to have at least one quantum of bending excitation, likely in combination with stretching vibrations. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468995
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