Rotational patches: Stark effect, dipole moment, and dynamics of water loosely bound to benzene

The geometry of the Fabry–Perot cavity makes it difficult to use for measuring the Stark effect. A “Stark cage” is described which generates an electric field suitable for this purpose. The cage is used to measure first and second order Stark splittings of several low-J transitions of the benzene-water dimer previously reported [Gutowsky, Emilsson, and Arunan, J. Chem. Phys. 99, 4883 (1993)]. The dipole moment is found to depend somewhat on rotational state, ranging from 1.65 to 2.00 Debye for both ground m=0 and first excited m=1 internal rotation states of the dimer. Additional m=1 transitions are reported, including the previously missing downshifted line of a k=0′ doublet. Its presence and various Stark effects require reassignment of the m=1 spectrum. The results demonstrate that each J→J+1 spectrum consists of three distinct components which arise from the H2O in an unusual way. In addition to the k-doublets, there are two progressions; a set of (J+1) negative k’s running from −J to 0, and a set of ...