A combined vibrational close‐coupling and rotational infinite order sudden technique is described for calculating vibrational excitation cross sections σvv′ for the three‐dimensional collisions of atoms with linear triatomic molecules. The method treats anharmonic, Coriolis, and vibrational angular momentum terms in the molecular Hamiltonian accurately, and is applicable to any realistic potential energy surface expressed in numerical or functional form. Application of the method to X–CO2(v1v2λv3) collisions, where X = He, Ne, or Ar, is described. An accurate anharmonic CO2 potential, expressed in terms of bond and angle displacements, is employed. The X–CO2 interaction potentials are more approximate and are expanded in terms of atom–atom pair potentials. Calculations of σvv′, over a grid of energies sufficient to give rate coefficients kvv′ for transitions between the low‐lying states of CO2 for temperatures up to 300 K, have been performed. Propensities for particular collisional excitations involving ...

Quantum study of vibrational excitation in the three‐dimensional collisions of CO2 with rare gas atoms

A laser‐fluorescence technique is used to determine vibration‐to‐vibration energy transfer rates for relaxation of HCl (v=1) and DCl (v=1) by CH4 and CD4. The rates of subsequent vibration‐to‐rotation and translation relaxation of the bending vibrations of CH4 and CD4 by several collision partners are measured. These data are interpreted in terms of a model which includes rotational motion of both collision partners, as well as relative translational motion. The variation of deactivation probabilities with the mass parameter, (μ†)−1=m−1+A1(μR1)−1+A2(μR2)−1, and temperature qualitatively indicates the relative importance of rotation and translation in each deactivation process.

Model for V→ T, R relaxation: CH4 and CD4 mixtures

The shock tube as wave reactor for kinetic studies and material systems

: A comprehensive survey of relaxation rate data important in the modeling of nonequilibrium infrared radiation from exhaust plumes at altitude is presented. A model is developed which considers energy transfer among the first fourteen vibrational states of CO2, the first five of H2O, and up to the first three states of each of the diatomic molecules considered, i.e., of N2, O2, CO, OH, and H2. Available data are first assembled for those processes that have been subjected to experimental analysis. Where possible, statistical and/or quantum considerations are used to relate unmeasured rate constants to those whose values are known. Finally, resort is made to available theory to obtain estimates for the rate constants for the balance of the interactions important to the overall model.

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A Survey of Vibrational Relaxation Rate Data for Processes Important to CO2-N2-H2O Infrared Plume Radiation

Rates of (V–V) vibrational energy transfer from the CO2 (0001) level to the levels of the bending (b) and symmetric (s) stretching modes and from these two modes to translation–rotation (V–T) are measured for CO2 deactivated by monatomic gases between 153 and 393 K by a photoacoustic method. This technique is complementary to experiments involving fluorescence quenching or ultrasonic dispersion and makes possible a better analysis of the details of vibrational exchange processes. In the temperature range under study the variation in the (V–T) rate constants appears to be considerably less than semiclassical theories might lead us to believe even if attractive forces are accounted for. The hypothesis in favor of transfer to the rotation of CO2 at low temperatures permits a better approach to experimental results, but nevertheless remains insufficient. For the cases of deactivation by all the inert gases except helium, the experimental results lead to retaining three dominant (V–V) transfer processes: (0001...

A photoacoustic study of intramolecular energy transfer in CO2 deactivated by monatomic gases between 153 and 393 K

times and that during the approach to equilibrium the relaxation time changes in the way to be expected from the change in the translational temperature. These observations have been confirmed by infrared measurements on shock heated CO2 (Hodgson & line i969) and are consistent with recent laser fluorescence measurements on the rate of deactivation of the asymmetric stretching mode (Hocker, Kovacs, Rhodes, Flynn & Javan i966; Moore, Wood, Ho & Yardley i967). In the present paper results are given for the relaxation times of C02 in an atmosphere of N2, Ne, He, D2 and H2. The object of these experiments was to measure relaxation times over a wide range of temperatures for these collision partners. The results give some insight into the relative importance of the effeets of the reduced masses and force fields at different temperatures. They provide the grounds for testing current calculations of relaxation times and help in the understanding of the collision processes important in the CO2 laser.

A shock tube study of vibrational relaxation in pure CO2 and mixtures of CO2 with the inert gases, nitrogen, deuterium and hydrogen

It has been shown that the probability for deactivating the bending mode of CO2 by H2, or D2 is in good accord with the theoretical calculations of Sharma (I969) at room temperature, but that the changes of probability with temperature are completely at variance with those calculated (Simpson & Chandler I970). The calculations were based on a model of rotational-vibrational energy transfer brought about by long-range forces and it was predicted that the probability would change by at least an order of magnitude at room temperature if para hydrogen were used instead of normal hydrogen. The present experiments on para hydrogen were undertaken to test the theory of Sharma and to try to understand the basis for the earlier experimental results.

C. J. S. M. Simpson

Papers

A shock tube study of vibrational relaxation in pure CO2 and mixtures of CO2 with the inert gases, nitrogen, deuterium and hydrogen

A study of vibrational-rotational energy exchange in a shock tube