Spectroscopic investigation of [Al,N,C,O] refractory molecules

Abstract

As of yet, unexamined aluminum bearing molecules may help elucidate aluminum chemistry and associated refractory atom reactions in the interstellar medium. The flexibility of modern quantum chemistry in the construction and analysis of novel molecules makes it perfectly suited to analyze molecules of astrochemical significance. In this paper, high level ab initio electronic structure calculations using the coupled cluster CCSD(T) and explicitly correlated coupled cluster CCSD(T)-F12 methods with large basis sets extrapolated to the complete basis set limit have been performed on the various [Al,N,C,O] isomers. The anharmonic rotational and vibrational spectroscopic parameters for all isomers are produced with these same levels of theory via quartic force fields and vibrational perturbation theory in order to aid in their potential laboratory or even astrophysical identification. The most stable isomer is determined here to be the aluminum isocyanate radical with linear equilibrium geometry AlNCO (X1Σ+). The NCO antisymmetric stretch of AlNCO has an intensity of 1500 km/mol, which should greatly aid in its infrared detection in the region around 2305 cm−1. Additionally, the AlOCN isomer is relatively low lying, possesses a 5.12 D dipole moment, and has a notable kinetic stability, making it a viable candidate for astronomical observation. All isomers are characterized by small frequencies, which indicates that these are floppy molecules. Isomers with a terminal aluminum atom are especially floppy, with bending modes less than 100 cm−1.

Spectral Signatures of Hydrogen Thioperoxide (HOSH) and Hydrogen Persulfide (HSSH): Possible Molecular Sulfur Sinks in the Dense ISM

“…However, due to the composite nature of the method, there are conflicting minima for the potential energy surface, thus introducing additional inaccuracy. This same inaccuracy has been seen as well for [Al, N, C, O] isomers [ 62 ]. While there is still considerable accuracy to experiment for the remainder of the fundamentals, the large amplitude motion of the torsion decreases the overall accuracy of the ground state rotational constants, seemingly preventing the accurate rovibrational modeling of this molecule.…”

Pathways to Detection of Strongly-Bound Inorganic Species: The Vibrational and Rotational Spectral Data of AlH2OH, HMgOH, AlH2NH2, and HMgNH2

“…Likely, the F12-TZ result is more correct since it relies upon a single level of theory. The composite CcCR has competing factors that can work against one another and provide spurious results for coordinates with flat potentials or where different levels of theory predict notably different minima (Morgan and Fortenberry, 2015;Bassett and Fortenberry, 2017;Trabelsi et al, 2019). The rotation of the O-H is small with a barrier of 3.3 kcal/mol for a relaxed F12-TZ scan of coordinate S 8 with step sizes of 2.0°.…”

Rotational Relaxation of AlNC and AlCN by para-H2 (j = 0) at Low Temperatures

“…21 However, its chemistry is not completely understood due to a lack of theoretical and experimental studies. 22 Of particular interest are the cyanide and isocyanide (CN/ NC) species because they are expected to be the major molecular carriers of metals in circumstellar gas. 23 AlNC 4,24 was detected in the outer circumstellar shell of IRC 10216, which is a cold region (T K ≈ 25 K).…”

“…Despite aluminum’s propensity to condense into grains, this element exhibits significant gas-phase chemistry . However, its chemistry is not completely understood due to a lack of theoretical and experimental studies …”