Fourier transform microwave spectrum of the CO-dimethyl sulfide complex

作者：Sato Akinori; Kawashima Yoshiyuki^*; Hirota Eizi

来源：Journal of Molecular Spectroscopy, 2010, 263(2): 135-141.

DOI：10.1016/j.jms.2010.07.010

• Van der Waals complex
• Isotopomers of CO-dimethylsufide
• Molecular structure
• Internal rotation
• Forbidden transition

The rotational spectrum of the CO-dimethyl sulfide (DMS) complex was measured in the frequency region from 4.8 up to 25 GHz by Fourier transform microwave spectroscopy. For the normal species 27 a-type and 57 c-type transitions were observed, while 16 and 8 c-type transitions were assigned for the species with (34)S and (13)C in the DMS moiety, respectively, in natural abundance. In addition, 7 a-type and 48 c-type transitions were assigned for the complex with the (13)CO enriched species as a component and 9 a-type and 42 c-type transitions for the complex with enriched C(18)O. No splitting was observed, which could be ascribed to the tunneling motion of the CO between two possible potential minima around DMS, while many transitions were split by the internal-rotation of the two methyl tops of the DMS unit. In cases where the K-type splitting was close to the methyl internal-rotation splitting, forbidden transitions were observed which apparently followed b-type selection rules. All of the observed transition frequencies for the normal species were analyzed simultaneously using a two-top internal-rotation and rotation Hamiltonian. The potential barrier height V(3) to internal rotation of the methyl groups of the DMS was determined to be 745.5 (30) cm(-1). The transition frequencies observed for all the isotopomers were analyzed using an asymmetric-rotor rotational Hamiltonian, to determine rotational and centrifugal distortion constants. The r(s) coordinates calculated from the observed rotational constants led to the conclusion that the CO moiety was located in a plane perpendicular to the skeletal plane of the DMS and bisecting its CSC angle. This structure of the CO-DMS is very much different from that of the CO-DME, in which the CO is located in the DME skeletal plane. The distance between the centers of gravity of the two moieties. R(cm), was calculated to be 3.789 angstrom for the CO-DMS, which is longer by only 0.11 angstrom than that in the CO-DME complex: 3.68 angstrom, in spite of the fact that the van der Waals radius of the S atom is much larger than that of the O atom. The small difference in R(cm) is, in part, ascribed to the location of the CO relative to the DMS/DME. The more important reason is that the intermolecular bonding of the CO-DMS is stronger than that of CO-DME: by assuming a Lennard-Jones-type potential, the force constant of the van der Waals stretching mode and the dissociation energy were estimated to be 2.7 Nm(-1) and 3.3 kJ mol(-1), respectively, which were larger than those of the CO-DME: 1.4 Nm(-1) and 1.6 kJ mol(-1).

• 出版日期2010-10