Theoretical rovibrational characterization of HAlNP: Weak bonding but strong intensities

Abstract

In the search for interstellar molecules containing at least one AlH bond, HAlNP may be a viable candidate for potential observation. The present high-level quantum chemical analysis shows that the 1 1A′ and 1 3A″ states of HAlNP are nearly degenerate (differ by ~20 cm−1). Additionally, this molecular connectivity is preferred over the resulting van der Waals AlH⋯PN isomer by 17.31 kcal/mol and has exceptionally bright itensities for fundamental infrared frequencies at 1763.2 cm−1 and 1261.6 cm−1 for the singlet as well as 1813.1 cm−1 and 1296.2 cm−1 in the triplet. These sets both fall in regions perceived to be dominated by hydrocarbon emissions, but the notable strengths of these infrared signals imply that this molecule or other third-row atom containing species cannot be fully neglected for inclusion as potential, astronomical, spectral carriers. 1 1A′ HAlNP also possesses a 0.95 D dipole moment and near-prolate behavior with a trusted CcCR Beff of 3066.2 MHz. The 1 3A″ state of HAlNP has a smaller dipole moment at 0.46 D and a slightly smaller Beff of 3056.8 MHz. Finally, the 1 1A′ state vibrational frequencies computed via two different coupled cluster approaches (CCSD(T)-F12/cc-pVTZ-F12 and CcCR) agree to, typically, within 2.5 cm−1 of one another giving future promise for the former’s use in larger molecules where CcCR is intractable.