Radiative lifetimes and cooling functions for astrophysically important molecules

TL;DR

This paper computes radiative lifetimes and cooling functions for key astrophysical molecules using extensive line lists, aiding models of stellar and planetary formation and linking laboratory data with astrophysical observations.

Contribution

It introduces detailed lifetime and cooling function calculations for molecules like SiO, CaH, AlO, ScH, H2O, and methane, based on the ExoMol line lists, highlighting unique long-lived states in methane.

Findings

Long-lived excited states in methane with no decay routes.

Cooling functions relevant for star and planet formation.

Data useful for maser models and laboratory comparisons.

Abstract

Extensive line lists generated as part of the ExoMol project are used to compute lifetimes for individual rotational, rovibrational and rovibronic excited states, and temperature-dependent cooling functions by summing over all dipole-allowed transitions for the states concerned. Results are presented for SiO, CaH, AlO, ScH, H$_2$O and methane. The results for CH$_4$ are particularly unusual with 4 excited states with no dipole-allowed decay route and several others where these decays lead to exceptionally long lifetimes. These lifetime data should be useful in models of masers and estimates of critical densities, and can provide a link with laboratory measurements. Cooling functions are important in stellar and planet formation.