Rotational spectra of mono-substituted asymmetric C6H6-H2O dimers

This paper reports the assignment of the rotational spectra of the m = 0 and 1 states of (CC5H6)-C-13-(HO)-O-2 and C6H5D-H2O dimers. The m = 1 progression was not identified or assigned for both (CC5H6)-C-13-H2O and C6H5D-H2O in the earlier work, though for the symmetric isotopomers (C6H6-H2O/D2O/(H2O)-O-18), they were identified [H.S. Gutowsky, T. Emilsson, E. Arunan, J. Chem. Phys. 99 (1993) 4883]. The m = 1 transitions for (CC5H6)-C-13-H2O and C6H5D-H2O were split into two, unlike that of the parent C6H6-H2O isotopomer. The splitting varied, somewhat randomly, with quantum numbers J and K. The m = 0 lines of (CC5H6)-C-13-H2O had significant overlap with the m = 1 lines of the parent isotopomer, clouding proper assignment, and leading to an rms deviation of about 200 kHz in the earlier work. The general semi-rigid molecular Hamiltonian coupled to an internal rotor, described recently by Duan et al. [Y.B. Duan, H.M. Zhang, K. Takagi, J. Chem. Phys. 104 (1996) 3914], is used in this work to assign both m = 0 and 1 states of (CC5H6)-C-13-H2O and C6H5D-H2O dimers. Consequently, the m = 0 fits for (CC5H6)-C-13-H2O/D2O have an rms deviation of only 4/7 kHz, comparable to experimental uncertainties. The fits for m = 1 transitions for (CC5H6)-C-13-H2O and C6H5D-H2O dimers have an rms deviation of about 200 kHz. However, it is of the same order of magnitude as that of the m = 1 state of the parent C6H6-H2O dimer. The A rotational constants determined from the m = 0 fits for both (CC5H6)-C-13-H2O and (CC5H6)-C-13-D2O isotopomers are identical and very close to the C rotational constant for (CC5H6)-C-13. This provides a direct experimental determination for the C rotational constant of (CC5H6)-C-13, which has a negligible dipole moment. (c) 2005 Elsevier Inc. All rights reserved.