Quantum nature of molecular vibrational quenching: Water - molecular hydrogen collisions

TL;DR

This study demonstrates that vibrational quenching of water by hydrogen is fundamentally a quantum process, with quantum effects dominating energy transfer mechanisms even at high energy levels, using first-principles quantum calculations.

Contribution

The paper provides the first fully quantum, converged calculations of water vibrational quenching rates by hydrogen, revealing the quantum nature of the process.

Findings

Quantum vibrational to rotational energy transfer dominates

Calculated quenching rates up to 500K for water-hydrogen collisions

Quantum effects persist despite large quantum level numbers

Abstract

Rates of conversions of molecular internal energy to and from kinetic energy by means of molecular collision allows to compute collisional line shapes and transport properties of gases. Knowledge of ro-vibrational quenching rates is necessary to connect spectral observations to physical properties of warm astrophysical gasses, including exo-atmospheres. For a system of paramount importance in this context, the vibrational bending mode quenching of H2O by H2, we show here that exchange of vibrational to rotational and kinetic energy remains a quantum process, despite the large numbers of quantum levels involved and the large vibrational energy transfer. The excitation of the quantized rotor of the projectile is by far the most effective ro-vibrational quenching path of water. To do so, we use a fully quantum first principle computation, potential and dynamics, converging it at all stages, in a full coupled channel formalisms. We present here rates for the quenching of the first bendingmode of ortho-H2O by ortho H2, up to 500K, in a fully converged coupled channels formalism.