Quantum dynamical resonances in low-energy CO(j = 0) + He inelastic collisions

Abstract

In molecular collisions, long-lived complexes may be formed that correspond to quasi-bound states in the van der Waals potential and give rise to peaks in the collision energy-dependent cross-sections. They are known as 'resonances' and their experimental detection remains difficult because their signatures are extremely challenging to resolve. Here, we show a complete characterization of quantum-dynamical resonances occurring in CO-He inelastic collisions with rotational CO(j = 0->1) excitation. Crossed-beam scattering experiments were performed at collision energies as low as 4 cm(-1), equivalent to a temperature of 4 K. Resonance structures in the measured cross-sections were identified by comparison with quantum-mechanical calculations. The excellent agreement found confirms that the potential energy surfaces describing the CO-He van der Waals interaction are perfectly suitable for calculating state-to-state (de)excitation rate coefficients at the very low temperatures needed in chemical modelling of the interstellar medium. We also computed these rate coefficients.

Observation of quantum dynamical resonances in near cold inelastic collisions of astrophysical molecules

“…Experimental observation of resonances is thus likely to provide a stringent test for the accuracy of the PES. Such quantum effects proved nonetheless very difficult to detect34 and could only be seen recently 24,25,27–29,33. The findings obtained in our laboratory are described in this mini review.…”

“The Even-Lavie valve as a source for high intensity supersonic beam”

“…The narrow time width indicates high Mach number of the beam (up to 50) so no appreciable heating of the beam occurs [35,58,59]. The excitation occurs inside the expansion nozzle where there are still many collisions in the gas.…”

Towards accurate quantum simulations of large systems with small computers

“…The standard ab initio programs solve the many-electron Schrödinger equations with predefined basis sets. For example, some well defined large basis sets are now widely used for accurate energy calculations18192021. However, for large systems, the limited capabilities of computers may force us to resort to small basis sets.…”