Rotational spectra, nuclear quadrupole hyperfine tensors, and conformational structures of the mustard gas simulent 2-chloroethyl ethyl sulfide

Rotational spectra have been recorded for both the ³⁵Cl and ³⁷Cl isotopic forms of two structural conformations of 2-chloroethyl ethyl sulfide (CEES). The rotational constants of the ³⁵Cl and ³⁷Cl isotopomers were used to identify the conformational isomers. A total of 236 hyperfine transitions have been assigned for 47 rotational transitions of the ³⁵Cl isotope of a GGT conformer, and 146 hyperfine have been assigned for 37 rotational transitions of the ³⁷Cl isotopomer. For the second conformer, a total of 128 (110) hyperfine and 30 (28) rotational transitions have also been assigned to the ³⁵Cl (³⁷Cl) isotopes of a TGT conformation. The extensive hyperfine splitting data, measured to high resolution with a compact Fourier transform microwave spectrometer, were used to determine both the diagonal and off-diagonal elements of the ³⁵Cl and ³⁷Cl nuclear quadrupole coupling tensors in the inertial tensor principal axis system. The experimental rotational constant data, as well as the ³⁵Cl and ³⁷Cl nuclear quadrupole coupling tensors, were compared to the results from 27 optimized ab initio (HF/6-311++G^∗∗ and MP2/6-311++G^∗∗) model structures.