### Abstract

A generalized cumulant expansion method is developed for applying stochastic reductions to molecular collision processes. We begin by introducing an approximate partitioning of a collision system into two subsystems S _{r} and S_{i} which are assumed to be weakly correlated. Cumulant expansion methods are then used to simultaneously perform a stochastic reduction over S_{i}, and a projection of the diagonal elements of the reduced density matrix for S_{r} thereby leading to a Pauli master equation describing S_{r}. We then apply this general equation using an impulse approximation partitioning to problems in inelastic V-T and R-T scattering. For He+ H_{2} vibrationally inelastic collisions, the stochastic theory predicts low order moments and some probabilities in very good agreement with exact quantum results. In applications to He+ H_{2} rigid rotor scattering, integral cross sections and opacity functions within 10%-30% of exact results are obtained at most energies.

Original language | English |
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Pages (from-to) | 5220-5225 |

Number of pages | 6 |

Journal | Journal of Chemical Physics |

Volume | 66 |

Issue number | 11 |

Publication status | Published - 1977 |

### ASJC Scopus subject areas

- Atomic and Molecular Physics, and Optics