Collisional Excitation and Weak Maser Action of Interstellar Methanimine

TL;DR

This study calculates the excitation rates of interstellar methanimine using quantum mechanics, predicts weak maser emissions, and confirms these predictions with observations, advancing understanding of molecular excitation in space.

Contribution

It introduces a new high-accuracy potential energy surface for methanimine and models its non-equilibrium spectrum, including maser action, in interstellar clouds.

Findings

The $1_{10} o 1_{11}$ transition at 5.29 GHz is inverted.

Predicted weak maser emission matches Green Bank Telescope observations.

Provides detailed quantum mechanical excitation data for interstellar methanimine.

Abstract

The inelastic cross sections and rate coefficients for the rotational excitation of methanimine (CH$_2$NH) by cold H$_2$ have been determined quantum mechanically based on a new highly correlated five-dimensional potential energy surface. This surface was fitted to more than 60 000 ab initio points with a root mean square error of $\sim$ 1-2 cm$^{-1}$ in the region of the potential well whose depth is -374.0 cm$^{-1}$. The rotationally inelastic rate coefficients have been combined with spectroscopic data to generate the non-equilibrium spectrum of CH$_2$NH towards the interstellar molecular cloud Sgr~B2(N). The transition $1_{10}\to 1_{11}$ at 5.29 GHz is found to be inverted and the predicted weak maser emission spectrum is in excellent agreement with new observations performed with the 100-meter Green Bank Telescope.