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

Aluminium hydroxide (AlOH) is ubiquitous in the interstellar medium. However, there are no reliable data available in the literature that can be used to interpret the observations. Therefore, in this paper, we deal with the rotational rate coefficients of AlOH induced by collision with helium. The potential energy surface of the AlOH-He complex was computed within the coupled cluster ab initio method with single, double and perturbative triple excitation, in conjunction with the augmented-correlation consistent-polarized valence quadruple zeta Gaussian basis set. Using this potential energy surface, we computed rotational cross-sections for total energies ranging up to 1500 cm −1 with the close-coupling approach. By thermally averaging these cross-sections over the kinetic temperature range 5-300 K, we derived the AlOH rate coefficients corresponding to the first 13 rotational levels. Propensity rules have been found in favour of | j| = 1. The data calculated in this paper have been compared with previous results and significant differences are observed. Such a finding might greatly affect the calculation of the AlOH abundance. In addition, this might encourage experimental work to settle the matter.