State-to-State Differential and Relative Integral Cross Sections for Rotationally Inelastic Scattering of H2O by Hydrogen

TL;DR

This study measures and analyzes the differential cross sections for rotationally inelastic scattering of water by hydrogen, comparing experimental results with quantum scattering calculations to validate theoretical models.

Contribution

It provides the first detailed experimental measurements of state-to-state differential cross sections for H2O-H2 collisions and compares them with advanced quantum calculations.

Findings

Excellent agreement between experimental data and quantum predictions.

Validated the accuracy of the H2O-H2 potential energy surface.

Provided detailed angular distributions for specific rotational states.

Abstract

State-to-state differential cross sections (DCSs) for rotationally inelastic scattering of H2O by H2 have been measured at 71.2 meV (574 cm-1) and 44.8 meV (361 cm-1) collision energy using crossed molecular beams combined with velocity map imaging. A molecular beam containing variable compositions of the (J = 0, 1, 2) rotational states of hydrogen collides with a molecular beam of argon seeded with water vapor that is cooled by supersonic expansion to its lowest para or ortho rotational levels (JKaKc= 000 and 101, respectively). Angular speed distributions of fully specified rotationally excited final states are obtained using velocity map imaging. Relative integral cross sections are obtained by integrating the DCSs taken with the same experimental conditions. Experimental state-specific DCSs are compared with predictions from fully quantum scattering calculations on the most complete H2O-H2 potential energy surface. Comparison of relative total cross sections and state-specific DCSs show excellent agreement with theory in almost all details