Structure of the nitrosomethane molecule (CH₃NO) in the ground electronic state: Testing of ab initio methods for the description of potential energy surface

Abstract

ABSTRACT:The equilibrium geometry, barrier to internal rotation, and harmonic and anharmonic vibrational frequencies of the CH 3 NO molecule in the ground electronic state were calculated by different modern quantum chemical techniques. Special attention was given to the problem of torsional motion. The dependence of the results of calculations on the atomic orbital and molecular orbital basis sets and correlated methods was examined. The results of calculations were compared with experimental data. Some methods provided excellent agreement with the experiment.

Theoretical study of prebiotic precursors: the peptide bond and its silicon, sulphur and phosphorous analogues

“…For example, the assignment of the CH 3 rock to a band at 916 cm x1 , which is dubious in view of the large discrepancy with the theoretical values obtained in the present DFT calculations and numerous high-quality post-SCF treatments (Dolgov et al 2004), has been revised and associated to the band at 967 cm x1 . As for formamide, seven high-frequency vibrations are found in the region 3100-1200 cm x1 of the vapour phase spectrum.…”

One-dimensional models of internal rotation in CX3NO molecules (X=H, D, F)

“…In most cases, the MR-AQCC/cc-pVTZ method (introduced recently by Szalay and Bartlett, see [27]) with the use of the active space which is constructed from four MOs, p NO , p NO* , n + , and n À , occupied by six electrons, (for more details, see [24][25][26]), provides nearly spectroscopic accuracy [25]. However, this method is too laborious.…”

“…The AOs were constructed using a spherical harmonic basis set. Because of this, the estimates obtained in the present study are slightly different from those reported in the studies [24,26]. Calculations by the MR-AQCC method were performed using the quantum-chemical program system COLUMBUS [29][30][31][32].…”

“…Calculations by the MP2 method were carried out using the GAMESS (US) program package [28]. The accuracy of calculations of molecular integrals was improved compared to the earlier studies [24,26]. The AOs were constructed using a spherical harmonic basis set.…”

“…Earlier [24][25][26], we have calculated the structures of the CH 3 NO and CF 3 NO molecules in the ground and lowest excited electronic states using various ab initio quantum-chemical methods and analyzed the reliability of different approximations as applied to the systems under study. In most cases, the MR-AQCC/cc-pVTZ method (introduced recently by Szalay and Bartlett, see [27]) with the use of the active space which is constructed from four MOs, p NO , p NO* , n + , and n À , occupied by six electrons, (for more details, see [24][25][26]), provides nearly spectroscopic accuracy [25].…”