Rotationally inelastic scattering of NH3 with H2: Molecular-beam experiments and quantum calculations

Abstract

In crossed molecular-beam experiments, three type of cross sections have been measured: Total differential cross sections with well-resolved diffraction oscillations for oD2–NH3 at E=95.9 and 111.3 meV, differential energy-loss spectra for ND3–oD2 at E=118.3 meV which cover the center-of-mass (c.m.) angular range from 85° to 170° and are obtained by time-of-flight (TOF) analysis, and state-to-state integral cross sections for oNH3–H2 and pNH3–H2 at E=75 meV for many final rotational states which are detected by resonance enhanced multiphoton ionization. These data which are mainly sensitive to the anisotropy of the potential energy surface are well reproduced by quantum calculations in the coupled-states approximation. The potential is constructed by combining large basis-set self-consistent-field (SCF) calculations with damped long-range dispersion coefficients. The two free parameters of the damping function are fitted to a restricted set of configuration interaction (CI) calculations.

Inelastic collisions of interstellar molecules

“…3 the measured cross sections for transitions induced by collisions with H2 are presented. In the same figure also theoretical values of Ebel et al (1990) and of Offer & Flower (1990) to the lo state is now the strongest one, as predicted also by theory. For para-NH3 there is a strong preference for the excitation to the lower 2i state, in agreement with theory.…”

Rotationally Inelastic Scattering of Quantum-State-Selected ND3with Ar

“…Prior study of rotational energy transfer in collisions of ammonia isotopologues with He and H 2 has been motivated by astrophysical applications, − as discussed in our recent paper . To complement such studies and to examine the effects of changes to the properties of the collision partner on the collision dynamics, inelastic scattering of NH 3 with Ar has also been the subject of extensive previous experimental investigation. − This paper presents the first quantum state-to-state resolved differential cross sections (DCSs), as well as calculated integral cross sections (ICSs) for the ND 3 + Ar system.…”

Rotationally inelastic scattering of CD3 and CH3 with He: comparison of velocity map-imaging data with quantum scattering calculations

“…ICSs have also been reported for rotationally inelastic collisions of NH 2 with He. 41 Greater attention has been paid to the inelastic scattering of closed-shell triatomic and polyatomic molecules, as illustrated by determinations of DCSs for scattering of ammonia [42][43][44] and deuterated ammonia 45 with rare gases and molecular hydrogen, and for water with helium 46 and hydrogen. 47 Along with advances in experimental techniques, there have been many quantum scattering calculations of ICSs, and also DCSs, employing high-quality potential energy surfaces (PESs).…”

“…These have mostly concerned collisions of diatomic and stable polyatomic molecules. 14,18,21,[25][26][27][28][30][31][32][33]42,[46][47][48] Dagdigian 49 recently reviewed work on quantum scattering calculations of collisional rotational and vibrational energy transfer in small hydrocarbon intermediates and highlighted studies involving methylene (CH 2 ) 50,51 and methyl. 52,53 The pathways for energy transfer in collisions of a polyatomic are more complicated than for collisions of a diatomic molecule.…”