New ab initio calculations and collisional properties of closed-shell NCCP (1Σ+) by collisions with He (1S)
Abstract
NCCP, a phosphorous species, is believed to have been discovered in the carbon-rich star IRC+10216. Understanding collisional properties, such as cross-sections ($\sigma _{j\rightarrow j^{\prime }}$) and rate coefficients ($k_{j\rightarrow j^{\prime }}$), is important for the reliable determination of molecular abundance. The non-reactive collisions between NCCP and He species at low temperatures are the subject of this study. Calculations are based on new ab initio potential energy surface (PES) of NCCP-He. The PES calculations are carried out at the CCSD(T)-F12a in conjunction with the aug-cc-pVTZ basis set. The PES is found to have a global minimum towards the N end with a well depth of -46.40 cm-1. The ab initio points are analytically fitted on to the Legendre polynomial relevant for quantum scattering. From this fitted PES, the integral inelastic rotational cross-sections of NCCP with He collisions are computed for total energies up to 550 cm-1, using the accurate close coupling approach of quantum mechanics. The resonances are observed at low total energies due to quasi-bound states of the NCCP-He complex. Rate coefficients are determined among the 19 lowest rotational levels of NCCP by thermally averaging the cross-sections at low temperatures. The de-excitation rate coefficients increase with decreasing Δj.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2022
- DOI:
- 10.1093/mnras/stac2063
- Bibcode:
- 2022MNRAS.515.5145R
- Keywords:
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- astrochemistry;
- molecular data;
- scattering;
- ISM: abundances;
- ISM: molecules