Articles you may be interested inQuantum scattering studies of inelastic collisions of NH(A 3Π) with helium: Finestructure and Λdoublet propensities J. Chem. Phys. 95, 5036 (1991); 10.1063/1.461792Quantum theory and collisional propensity rules for rotationally inelastic collisions between polyatomic molecules (NH3 and CO2) and an uncorrugated surfaceThe observed and ab initio calculated propensity rules for collisions of NH 3 with rare gas atoms are found to be in reasonable agreement for NH 3 -Ar, whereas for NH 3 -He they show large discrepancies. In order to examine these discrepancies we have calculated state-to-state integral cross sections for collisions of NH 3 with He using the close coupling method. The NH 3 -He interaction potential has been obtained from SCF calculations, augmented by a multipole-expanded damped dispersion energy. Our calculations show that the discrepancies can be accounted for if the cross sections are corrected for the imperfect initial state preparation in the experiment. They also clarify why the discrepancies do not occur to the same extent for NH 3 -Ar. After comparing our new theoretical results with the experimental data we found that for one experimental cross section for NH 3 -He the earlier assignment must be corrected.
By means of the close coupling method we have calculated state-to-state differential and integral cross sections for rotational excitation and inversion of NH3 by collisions with Ar and He. For NH3–Ar we used an empirical and a scaled ab initio potential, for NH3–He an ab initio potential. The differential cross sections for NH3–Ar obtained from the empirical potential have an angular dependence that is in closer agreement with experiment than those obtained from the scaled ab initio potential. The integral cross sections are reproduced equally well by the two potentials. Also for NH3–He the differential cross sections are in accordance with experiment. For the integral cross sections the agreement is good too, except for the very small cross sections to some of the higher rotationally excited states. For both complexes the differential cross sections show a strong dependence on energy, both in their angular dependence and in their relative magnitudes.
Quantum mechanical calculations have been performed to study the fragmentation dynamics of the A r-N H 3 van der Waals complex excited in the v2 ("umbrella") vibrational level with i>2= l . Vibrational predissociation has been investigated for different initial quasibound states, corresponding to excitation in the stretching or bending van der Waals levels or in the tunneling motion of the NH3 umbrella inversion, for both ortho and para varieties of NH3, and for three values of the total angular momentum J and its projection i l onto the intermolecular axis, C/,il) = (
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