Converged close-coupling and coupled-states calculations were used to obtain state-to-state rate constants and pressure broadening coefficients for the collisional rotational (de-)excitation of C2H2 by He. The ab initio potential used in these calculations was previously computed by symmetry-adapted perturbation theory. The computed pressure broadening coefficients and total rate constants agree well with the available experimental data. In the experimental part of the paper stimulated Raman-pumping has been used to prepare acetylene in selected rotational states (ji=2 to 18 and ji=1 to 19 of the C≡C stretching mode). The population decay in the prepared state and the transfer to other rotational states was monitored by laser induced fluorescence. The experimental data can be described by an infinite-order-sudden power law (IOS-P) or directly compared with the ab initio derived rate constants. The influence of multiple collisions possible at the relatively large pressure-delay-products employed has been taken into account by simulating the rotational energy transfer with a master equation. Experimentally we obtain a total rate constant for depopulation of ktot=10.89±0.07μs−1 Torr−1 and IOS-P fitting parameters of A=5.58 and γ=0.96 in very good agreement with the ab initio calculated values. There we obtain ktot=10.69±0.09μs−1 Torr−1 and IOS-P fitting parameters of A=6.18 and γ=0.96. Also the experimental state-to-state rotational energy transfer constants, which vary from 5.83 to 2.32 μs−1 Torr−1 for endothermic Δj=2 collisions, agree very well with the ab initio data.

Articles you may be interested inErratum: "Direct determination of state-to-state rotational energy transfer rate constants via a Raman-Raman double resonance technique: ortho-acetylene in v2 = 1 at 155 K" [J. Chem. Phys.132, 154303 (2010)] J. Chem. Phys. 134, 139902 (2011); 10.1063/1.3575199Rate coefficients for reaction and for rotational energy transfer in collisions between CN in selected rotational levels ( X Σ + 2 , v = 2 , N = 0 , 1, 6, 10, 15, and 20) and C 2 H 2 Fate of isolated CH (B 2 Σ − ,v=0,J) states in inelastic collisions with CO

Fate of isolated CH (B 2 Σ − ,v=0,J) states in inelastic collisions with CO

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