Molecular Structure and Characteristics of Methyl Mercaptan Under External Electric Field

Abstract

The reaction of methyl mercaptan (CH₃SH) with groups such as ^•OH, O^•, and SO₂ in the air forms acid rain and photochemical smog, which damage the atmosphere seriously. It is found that methyl mercaptan can be degraded effectively by studying its dissociation characteristics of it in an external electric field. The total energy, C–S bond length, HOMO–LUMO energy gap, electric dipole moment, as well as charge distribution, IR spectrum, and dissociation potential energy surface of methyl mercaptan molecule under external electric field (0–12.5 V nm^–1) were studied by density functional theory (DFT) at B3LYP/6-311++(d,p) basis set level. Moreover, the UV–Vis absorption spectrum of methyl mercaptan with the external electric field was obtained by CIS/6-311++(d,p) method. The calculation results show that along the direction of the C‒S bond line, the molecular system energy gradually decreases, while the C–S bond length increases gradually. Meanwhile, the dipole moment monotonously decreases with the field, and the HOMO–LUMO energy gap E_G monotonically decreases after a slight increase at the beginning with the increase of the field. When the applied external electric field is gradually enhanced, the barrier of the C–S bond of methyl mercaptan molecule is reduced. It shows that when the employed external electric field strength arrives at 21.91 V nm^–1, the C–S bond can be broken completely, that is, methyl mercaptan is degraded.