Collision induced rotational excitation of AlF (X 1Σ+) by para-H2 (j=0)

Abstract

Rotational excitation cross sections and rate coefficients of AlF collisions with para-H 2 are computed at low temperature, i.e., for T ≤ 70 K. Prior to collisional calculations, a four-dimensional (4D) potential energy surface (PES) for the AlF-H 2 system is calculated at the ab initio Coupled-Cluster level of the theory with an aug-cc-pVQZ Gaussian basis set. This 4D-PES is further reduced to a twodimensional (2D) PES based on the considerations related to collisional studies with para-H 2 . The [Al-F] and [H-H] bond lengths are frozen at their experimental equilibrium value r e = 1.654369 bohr and r e = 1.4011 bohr respectively. The interaction energy presents a global minimum located ∼63 cm −1 below the AlF-H 2 dissociation limit. With this PES, cross sections are determined in the Close-Coupling (CC) approach and rate coefficients are inferred by averaging the cross sections over a Maxwell-Boltzman distribution of kinetic energies. These quantities are significantly magnified in comparison with their AlF-He counterparts. The already observed propensity towards J = 1 transitions for AlF-He remains.

Astronomical detection of radioactive molecule 26AlF in the remnant of an ancient explosion

“…Also, the excitation temperature of AlF derived here is consistent with the kinetic temperature constrained from the single-dish survey (12). Using collision rates of AlF with p-H 2 and with He at 10 K (39,40), we calculated critical densities for all observed transitions. They range from 10 4 cm -3 for J=1-0 to 10 7 cm -3 for J=7-6 and are therefore comparable to critical densities of analogous transitions of low-density molecular tracers such as CO.…”

Cross-sections and rate coefficients for rotational excitation of aluminium hydroxide by helium

“…Such an estimation was justified in early works on heavy molecules, such as SiS (Lique et al 2008) and SO (Lique et al 2007). However, this approximation was not valid for many other systems, including relatively light molecules, (Gotoum et al 2012;Lanza et al 2014;Najar et al 2017). As a result, the present study provides an opportunity to study the collisional de-excitation of AlOH by H 2 .…”

ATOMIUM: halide molecules around the S-type AGB star W Aquilae

“…For the collisional rates, a new calculation was performed to obtain rates for sufficiently high temperatures as seen in our circumstellar model. This calculation is an extension of the earlier work by Gotoum et al (2012), in which rates were given for temperatures up to 70 K. Using the potential energy surface (PES) for AlF-H 2 given by Gotoum et al (2012), we broadened the calculations of the integral cross sections for kinetic energy up to 10000 cm −1 . Indeed the earlier work was limited for total energy E c ≤ 350 cm −1 where cross sections were calculated in the quantum mechanical close coupling formalism (CC, Arthurs & Dalgarno 1960).…”