Theoretical spectroscopic characterization at low temperatures of methyl hydroperoxide and three S-analogs

Abstract

The low temperature spectra of the detectable species methyl hydroperoxide (CH3OOH) and three sulfur analogs, the two isomers of methanesulfenic acid (CH3SOH and CH3OSH) and the methyl hydrogen disulfide (CH3SSH), are predicted from highly correlated ab initio methods (CCSD(T) and CCSD(T)-F12). Rotational parameters, anharmonic frequencies, torsional energy barriers, torsional energy levels, and their splittings are provided. Our computed parameters should help for the characterization and the identification of these organic compounds in laboratory and in the interstellar medium.

The torsional states of methyl hydroperoxide molecule calculated using anharmonic zero point vibrational energy

“…0 0 + A 1 0.000 0.000 0.000 0.000 0.000 0.000 0 0 + A 1 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Analysis of the data given in columns 2 and 4 of table 1 indicates excellent agreement in the values of the calculated energies of torsional states of the hydroxyl group obtained in this work and in [19], despite the different approaches to compiling the vibrational Schrӧdinger equation and a different number of points, in which the calculations of the potential energy were carried out. Comparable inferences can be made by analysing the data in columns 2 and 7 of table 2, where the calculations took into account the ZPVE in the harmonic approximation at the MP2/Aug-cc-pVTZ level of theory.…”

“…It was found that the tunneling of the hydroxyl group in the ground state occurs at a frequency of 14.97 cm -1 , while the corresponding tunneling frequency of the methyl group was 7.64 ⋅ 10 -5 cm -1 . Recently [19], a more deep and detailed theoretical study of torsional vibrations in the MHP molecule was carried out. 2D potential energy surface (PES) for two torsional coordinates was calculated at a high level of theory (CCSD(T)/Aug-cc-pVTZ).…”

Structural and spectroscopic characterization of methyl isocyanate, methyl cyanate, methyl fulminate, and acetonitrile N-oxide using highly correlated ab initio methods

“…9 For the remaining structures, the angles between the heavy atoms are the following: C3N1C2 = 136. The CCSD(T)-F12/AVTZ-F12 equilibrium rotational constants of Table II were employed to determine the corresponding ground state parameters with the straightforward formula [26][27][28][29] B 0 = B e + ∆B core e + ∆B vib ,…”

“…4 A better agreement is obtained with the parameters fitted by Koput 18 and Halfen et al, 3 although the differences |A 0 ab initio − A 0 exp | = 2315 MHz 18 and |A 0 ab initio − A 0 exp | = 2231 MHz 3 are too large if we compare them with the usual accuracy found when CCSD(T)-F12 theory is applied. [26][27][28][29] This method usually provides a precision of few MHz.…”

“…In this paper, we use explicitly correlated ab initio methods that usually provide very accurate rotational and torsional parameters [26][27][28][29] for a theoretical characterization of the C 2 H 3 NO isomers at low temperatures. Equilibrium structures, vibrational frequencies, and rovibrational parameters are determined.…”