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The effect of para -hydrogen (j p = 0) collisions on the rotational de-excitation transitions of molecule NCCP is investigated in this study. The scattering information is obtained by spherically averaging a four-dimensional potential energy surface (4DPES) over various H2 molecule orientations. The calculations used the CCSD(T)-F12a method and aug-cc-pVTZ basis set to generate a 4DPES for the NCCP–H2 van der Waals system. Within the NCCP– para -H2 4DPES, a minimum energy point of 191.82 cm−1 is attained at a distance of 3.6 Å from the centre of mass of H2 and NCCP. To compute cross-sectional data for NCCP interacting with para -H2 (j p = 0), close coupling calculations are employed, encompassing total energies up to 600 cm−1. The resulting rate coefficients [ |$k_{j{\rightarrow }j^{\prime }}(T$|⁠)] are calculated across a temperature range spanning from 5 K to 200 K. In accordance with propensity, even Δ j = −2 transitions are highly preferred. Comparatively, the derived |$k_{j{\rightarrow }j^{\prime }}(T$|⁠) for NCCP–H2 are determined to be 1.5–4.5 times of NCCP–He. This observation implies that relying on a scaling factor of 1.38 to extrapolate rate coefficients for H2 collisions from those of NCCP–He is not a reliable approach. [ABSTRACT FROM AUTHOR]

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 Δ j. [ABSTRACT FROM AUTHOR]