Ab initio calculations and analysis of the torsional spectra of dimethylamine and dimethylphosphine

Abstract

In the present paper, ab initio calculations at MP2/RHF level are performed with different basis sets 6-31G(d,p), 6-311G(d, p), and 6-311(d f ,p) to determine the potential energy functions, the kinetic parameters, and the dipole moment components as a function of the double methyl rotation in dimethylamine ͑DMA͒ and dimethylphosphine ͑DMP͒. From the potential energy and kinetic parameters, the torsional energy levels and torsional functions are determined, and from the dipole moment variations, the far infrared spectra are synthesized by calculating both the frequencies and the intensities. The results are in relatively good agreement with experimental spectra. Calculations confirm the assignments performed with the experimental potentials fitted with only five terms. The calculations, however, allow to reassign the observed band at 239.8 cm Ϫ1 in DMA and at 177.2 cm Ϫ1 in DMP to the superimposition of two different transitions: the 03→04 third sequence and an 10→11 vibrationally excited fundamental.

Theoretical spectroscopic characterization at low temperatures of detectable sulfur-organic compounds: Ethyl mercaptan and dimethyl sulfide

“…Energy levels are referred to the torsional ZPVE (226.898 cm −1 for ETSH and 187.066 cm −1 for DMS), and they are classified using the vibrational quanta and the irreducible representations of the G 6 and G 36 and DMS, respectively. 9, 10 For ETSH, assignments are very arduous because of the large density of interacting states lying at very low energies.…”

“…9,10 The effect of the O → S substitution is thus detailed, as it was done in previous papers where couples of analogs were treated and compared. [34][35][36] …”

A theoretical study of the inversion and rotation barriers in Methyl-substituted Amines

“…[15][16][17][18][19][20][21][22][23] The experimental investigations were obtained using electron diffraction, 15 microwave, 16,17 and infrared and Raman 18,19 spectra. Theoretically, the calculations have been carried out using ab initio methods up to MP4 level.…”

“…Theoretically, the calculations have been carried out using ab initio methods up to MP4 level. [20][21][22][23] The trimethylamine molecule has also received various experimental and theoretical studies. [24][25][26][27][28][29][30][31] The experimental data of the geometry, vibrational frequencies and internalinversion and rotational barriers were obtained using microwave, 24,26 infrared and Raman, 25,27 techniques and employing analysis of the ultraviolet absorption and fluorescence spectra.…”

“…As obtained to methylamine, all geometrical parameters are in good agreement with previous experimental 15, 16 and theoretical results. [21][22][23] In the planar structure, the H-C-N-C-H atoms are coplanar to the amine hydrogen atom, and in the ground state pyramidal structure, this amine hydrogen atom forms an angle of 53.4 degrees to the H-C-N-C-H plane. These results are in good agreement with the MP2/6-31G(d,p) value, equal to 55.2 degrees, and also with the experimental data of 54.6 degrees.…”