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Journal ArticleDOI

Near‐Resonant Vibration→Vibration Energy Transfer: CO2(υ3 = 1) + M → CO2(υ1 = 1) + M* + ΔE

01 Mar 1970-Journal of Chemical Physics (American Institute of Physics)-Vol. 52, Iss: 5, pp 2333-2340
TL;DR: In this paper, the laser-excited vibrational fluorescence technique has been used to determine the rate constants for deactivation of the asymmetric stretching vibration of CO2 in collisions with CO2.
Abstract: The laser‐excited vibrational fluorescence technique has been used to determine the rate constants for deactivation of the asymmetric stretching vibration of CO2 in collisions with CO2, CH4, C2H4, CH3F, CH3Cl, CH3Br, CH3I, BCl3, and SF6. Rates were determined as a function of temperature in the range 300–800°K. The large deactivation cross sections σ for the latter seven molecules decreased as the temperature T increased. For the latter six collision partners σ∝1 / T. This result is interpreted as a near‐resonant vibrational energy transfer process in which three vibrational quantum numbers change as the vibrational energy is shared between the collision partners.
Citations
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Journal ArticleDOI
TL;DR: For molecules with vibrational transition dipole moments, the energy transfer cross sections, σ vv, decrease rapidly with increasing vibrational energy discrepancy, ΔE as discussed by the authors, and their magnitudes at resonance are accurately fit by first order calculations using the transition-dipole interaction.
Abstract: Laser‐excited vibrational fluorescence measurements have given rates for nearly resonant vibrational energy exchange between the asymmetric stretch of CO2 and the stretching vibrations of 13CO2, N2O, CO, and 15N2 as a function of temperature and of 13CO and D2 at room temperature. For molecules with vibrational transition dipole moments the energy transfer cross sections, σ vv, decrease rapidly with increasing vibrational energy discrepancy, ΔE. Their magnitudes at resonance are accurately fit by first order calculations using the transition—dipole interaction, but that theory underestimates σ vv for Δ E ≥ 66 cm−1, especially at low temperatures. At resonance, σ vv is inversely proportional to temperature. As ΔE increases, σ vv decreases less rapidly with temperature (13CO2, Δ E = 66 cm−1), becomes temperature‐insensitive (N2O, Δ E = 125 cm−1), and finally increases with temperature (12CO, Δ E = 206 cm−1). It appears that rotation—translation coupling terms in the intermolecular potential operate simultan...

118 citations

Journal ArticleDOI
TL;DR: In this article, the rate constants for quenching of N2 A by ethane exhibit a strong increase with a rising vibrational quantum number, indicating strongly a collision induced intersystem crossing with the N2 B3Πg state.
Abstract: Following the excitation of nitrogen and nitrogen/additive mixtures by single electron pulses the metastable nitrogen A3Σu+ is detected in its vibrational levels v=0–7 by absorption spectroscopy. The additives are ethylene, ethane, and NO. In pure nitrogen the prevailing process is a vibration‐vibration (V‐V) energy transfer process of the N2 A, v≥2 with Δv=2 to groundstate nitrogen. The rate constants increase with higher quantum numbers i.e., improving energy resonance up to a limiting collisional efficiency for this process of 10−2. The kinetic behavior of the vibrational states v=5, 6, 7 indicates strongly a collision induced intersystem crossing with the N2 B3Πg state. The rate constants for quenching of N2 A by ethane exhibit a strong increase with rising vibrational quantum number. Ethylene is generally more reactive and shows no strong dependence on the vibrational level. This is interpreted as a fast quenching of the electronic state by ethylene. While this latter process is relatively slow with ...

100 citations

Journal ArticleDOI
TL;DR: A review of recent applications of various theories of nonreactive collisions between diatomic molecules, from semiclassical to quantal, are surveyed in light of experimental data as discussed by the authors, providing the theoretician with a background of those features of the collision problems that require more accurate treatments, and to provide the experimentalist with a spectrum of models available for handling his data.
Abstract: The rapid progress in research on chemical lasers has led to increased interest in the development of theoretical models of molecular relaxation processes. In this review, recent applications of various theories of nonreactive collisions between diatomic molecules, from semiclassical to quantal, are surveyed in light of experimental data. The intention is to provide the theoretician with a back-ground of those features of the collision problems that require more accurate treatments, and to provide the experimentalist with a spectrum of models available for handling his data.

99 citations

Journal ArticleDOI
TL;DR: In this article, the laser-excited vibrational fluorescence method was used to measure cross-sections for gaseous CO2 with one quantum of asymmetric stretching energy.
Abstract: Intramolecular vibration‐to‐vibration energy transfer cross sections have been measured for gaseous CO2 with one quantum of asymmetric stretching energy. Data were obtained using the laser‐excited vibrational fluorescence method. Results are given over the temperature range 298–800°K for the collision partners n‐H2, 3He, 4He, Ne, Ar, Kr, and Xe, and for p‐H2, HD, and D2 at 298°K. All cross sections increase with temperature; those for the rare gases depend only weakly on reduced mass. The cross sections for hydrogen are much larger than those for helium, and increase sharply as the reduced mass decreases. The simple form of transition probability as a function of velocity and intermolecular potential used in most theories of vibration–translation energy transfer does not adequately account for these results. Since equal cross sections are observed for n‐H2 and p‐H2, it is unlikely that energy is transferred into rotation of H2.

86 citations

Journal ArticleDOI
TL;DR: In this article, laser-excited vibrational fluorescence experiments on CO2 and N2O combination levels were performed using a tunable optical parametric oscillator and rate constants near gas kinetic were obtained and assigned to the near-resonant V→V transfer of an asymmetric stretching quantum.
Abstract: Laser‐excited vibrational fluorescence experiments on CO2 and N2O combination levels were performed using a tunable optical parametric oscillator. Rate constants near gas kinetic were obtained and assigned to the near‐resonant V→V transfer of an asymmetric stretching quantum. Stimulated emission occurring at 4.3 μ was observed during 2.7 μ excitation of CO2 to the (1001) combination level.

74 citations

References
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Journal ArticleDOI
TL;DR: In this article, the authors calculated the vibrational relaxation times in gases using an exponential repulsion in a one-dimensional model and derived the constants of the interaction potential by fitting it to the data of Hirschfelder, et al. The theoretical values for the relaxation times are 10 to 30 times shorter than the experimental ones, which difference may be accounted for by the use of the onedimensional model.
Abstract: Vibrational relaxation times in gases are calculated with the method of Zener using an exponential repulsion in a one‐dimensional model. The constants of the interaction potential are determined by fitting it to the data of Hirschfelder, et al. The great effect which some impurities have is accounted for either by their low mass and resultant high velocity or by ``near resonance'' transfers in which the vibrational quantum of the substratum is used partly to excite the vibration of the impurity, only the difference being transferred to translation. However, there are other impurities, the action of which cannot be explained in this manner. The theoretical values for the relaxation times are 10 to 30 times shorter than the experimental ones, which difference may be accounted for by the use of the one‐dimensional model. Macroscopic equations governing the more complex relaxation processes in polyatomic gases and gas mixtures are developed.

987 citations

Journal ArticleDOI
TL;DR: In this article, a generalized theory of collision broadening is developed, adequate for predicting line breadths in the microwave and infra-red regions, although it is limited to a classical picture of the relative motion of the colliding molecules as a whole.
Abstract: In this paper a generalized theory of collision broadening is developed, adequate for predicting line breadths in the microwave and infra-red regions. This theory differs from previous ones in taking into account transitions among quantum states caused by collisions, although it is limited to a classical picture of the relative motion of the colliding molecules as a whole. Formulas are derived for computing approximate line broadening collision cross-sections from known intermolecular interactions, and the results of the theory are successfully compared with experiments on self-broadening in the ammonia inversion spectrum and the vibrational band spectra of HCl and HCN. Some cases of foreign gas broadening in the microwave region are examined, but it is concluded that in general the Van der Waals interaction, commonly assumed to be the force important in causing foreign gas broadening, is not adequate to cause the observed broadenings. The more complicated types of forces which become important at short range would have to be taken into account to give good agreement with experiment in these cases.

894 citations

Journal ArticleDOI
TL;DR: In this article, the impact theory of Anderson has been used to calculate the widths of pressure-broadened spectral lines by using the impact matrix of the interaction matrix, which has been extended to include the effect of the nonresonant terms of interaction matrix.
Abstract: This report is mainly of a review and expository nature and has been prepared for the purpose of outlining in considerable detail the method of calculating the widths of pressure-broadened spectral lines by using the impact theory of Anderson. In section I, the general quantum mechanical result is derived. In section II the adiabatic approximations are discussed. In section III, Anderson's theory has essentially been repeated with some slight changes. In section IV, several cases of molecular interactions are treated. The calculations have been extended to include the effect of the nonresonant terms of the interaction matrix which are neglected in Anderson's work.

665 citations

Journal ArticleDOI
TL;DR: In this paper, the cross section for the near-resonant transfer of vibrational energy from CO2 to N2 was calculated for the isotopes 14N2 (ΔE = 18 cm−1) and 15N2, and the impact parameter (semi-classical) approximation was used, and it was assumed that the vibration transfer was caused by the interaction of the instantaneous CO2 dipole moment with the N2 quadrupole moment.
Abstract: The cross section for the near‐resonant transfer of vibrational energy from CO2(001) to N2(0), CO2(001) + N2(0)→CO2(000) + N2(1) + ΔE, is calculated for the isotopes 14N2 (ΔE = 18 cm−1) and 15N2 (ΔE = 97 cm−1). The impact parameter (semi‐classical) approximation is used, and it is assumed that the vibrational‐energy transfer is caused by the interaction of the instantaneous CO2 dipole moment with the N2 quadrupole moment. When proper account is taken of the rotational motions of the molecules it is found that in collisions of CO2 with 14N2 only the low rotational levels of the CO2 and N2 molecules contribute to Reaction (1). In collisions of CO2 with 15N2, only those rotational levels contribute which undergo transitions cancelling most of the relatively large (97 cm−1) vibrational‐resonance defect. For 14N2 below about 1000°K, where the cross section displays a negative temperature dependence, the results are in excellent qualitative and quantitative agreement with available experimental data, with no ad...

383 citations

Journal ArticleDOI
TL;DR: In this paper, the rate of near-resonant exchange of vibrational energy between CO2 and N2 (ΔE=18 cm−1) has been measured.
Abstract: Laser‐excited vibrational fluorescence measurements have been made on the asymmetric‐stretching vibrational level (00°1) of CO2. Vibration→vibration energy‐transfer rates from this level due to collisions with CO2 and with a number of other collision partners are presented. The rate of near‐resonant exchange of vibrational energy between CO2 and N2 (ΔE=18 cm−1) has been measured. The kinetics of the CO2 laser system are analyzed in terms of a three‐level scheme. Observed laser performance is compared with that calculated by use of collisional and radiative coupling rates observed in nonionized gases and of electron activation and deactivation rates estimated from CO2 discharge systems. In accordance with the scheme presented, the relative effectiveness of small amounts of added H2, D2, and He on laser output parallels their effectiveness in deactivating the lower laser level. The criteria for selecting molecules with vibrational‐energy‐level patterns likely to produce laser systems are outlined. Attempts ...

340 citations