Collisional excitation of interstellar PN by H2: New interaction potential and scattering calculations

Abstract

Rotational excitation of interstellar PN molecules induced by collisions with H 2 is investigated. We present the first ab initio four-dimensional potential energy surface (PES) for the PN-H 2 van der Waals system. The PES was obtained using an explicitly-correlated coupled cluster approach with single, double, and perturbative triple excitations [CCSD(T)-F12b]. The method of interpolating moving least squares was used to construct an analytical PES from these data. The equilibrium structure of the complex was found to be linear, with the H 2 aligned at the N end of the PN molecule, at an intermolecular separation of 4.2 Å. The corresponding well-depth is 224.3 cm −1 . The dissociation energies were found to be 40.19 cm −1 and 75.05 cm −1 for complexes of PN with ortho-H 2 and para-H 2 , respectively. Integral cross-sections for rotational excitation in PN-H 2 collisions were calculated using the new PES, and were found to be strongly dependent on the rotational level of the H 2 molecule. These new collisional data will be crucial to improve the estimation of PN abundance in the interstellar medium from observational spectra.

Theoretical study of the CO2–O2 van der Waals complex: potential energy surface and applications

“…As we have done in the past for other vdW linear dimers [32][33][34][35][36][37][38][39] an analytical representation of the 4D-PES was constructed using an automated interpolating moving least squares (IMLS) methodology, freely available as a software package under the name AUTOSURF. 40 As usual, 41,42 a local fit was expanded about each data point, and the final potential is obtained as the normalized weighted sum of the local fits.…”

“…Some of us have been involved in the construction of each of a large number vdW PESs for which both monomers are linear and hence the intermolecular interactions are 4D. These include: (OCS) 2 , 45 (CO) 2 , 46 (CO 2 ) 2 , 5,47 CO 2 –CO, 6,32 CO 2 –CS 2 , 48 CO–N 2 , 49 (NNO) 2 , 50 CO 2 –HCCH, 51 C 6 H − –H 2 , 52 HC 2 NC–H 2 , 53 O 2 –CO, 54 O 2 –HCl, O 2 –HF, H 2 –O 2 , O 2 –N 2 , 37,55 CO–HCCH, HNC 3 –H 2 , 53 HC 5 N–H 2 , 53 C 4 H − –H 2 , 38 C 2 H − –H 2 , MgCCH–H 2 , CF + –H 2 , 33 HCS + –H 2 , 39 NCCP–H 2 , PN–H 2 , 36 CO 2 –N 2 , 8,19,35 and O 2 –O 2 . 56,57 Four systems from that list include CO 2 , and six others include O 2 .…”

Fully quantum calculations of O2–N2 scattering using a new potential energy surface: Collisional perturbations of the oxygen 118 GHz fine structure line

“…As we have done in the past for other van der Waals dimers composed of linear monomer fragments, [74][75][76][77][78][79][80][81][82][83][84][85] an analytical representation of the PES was constructed using an automated interpolating moving least squares (IMLS) methodology, which is available as a software package under the name autosurf. 86 As usual, 87,88 a local fit was expanded about each data point, and the final potential is obtained as the normalized weighted sum of the local fits.…”

Quantum dynamics with ab initio potentials

“…7 PESs for systems involving more than three atoms are more challenging. For non-reactive scattering, fortunately, it suffices to construct the interaction potential between rigid monomers, as done by Desrousseaux et al 8 for the PN + H 2 system, by Ben Krid et al 9 for the CH 3 Cl + He system, and by Loreau et al for the H 2 O + HF complex. However, the involvement of vibrational…”

“…Gianturco et al 18 investigate the rotationally inelastic scattering between HeH + and He. Desrousseaux et al 8 study the rotational excitation of PN by collisions with H 2 . In addition, Mant et al 6 report vibrational quenching cross sections for CN − by He and Ar.…”