LVG analysis of amidogen radical (NH2) found in interstellar medium and in cometary material

Abstract

Amidogen (NH₂), a b-type asymmetric top molecule with electric dipole moment 1.82  ±  0.05 Debye, is detected in Sgr B2, in high-mass star-forming regions W31C (G10.6−0.4), W49N (G43.2−0.1), W51 (G49.5−0.4), G34.3+0.1, and in several comets. Because of two hydrogen atoms, each with nuclear spin 1/2, its rotational energy levels can be classified into ortho and para groups. We have not considered for fine structure splitting and hyper-fine structure splitting of rotational levels. For 15 rotational levels in the ground vibrational state, having energy up to 400 cm${}^{-1},$ for each specie, the energies of rotational levels, and Einstein A and B coefficients for radiative transitions between the levels are calculated, using accurate values of spectroscopic data. These radiative transition probabilities along with the collisional rate coefficients (obtained from a scaling law) are employed as input parameters for solving a set of statistical equilibrium equations coupled with the equations of radiative transfer for each group. Several emission lines produced by amidogen are found. For each species of NH₂, we have considered some strongest emission lines along with the observed one, which may help for identification of NH₂ in the interstellar medium (ISM) and in the cometary material.