OBSERVATION OF DELTA-VERTICAL-BAR-K-L-VERTICAL-BAR=3 TRANSITIONS IN THE NU(3) BAND OF H3O+

Although the vibration-rotation spectrum of H3O+ has been studied exte nsively, there has been no experimental information on the value of th e C rotational constant because of the absence of any observed Delta/k - l/ not equal 0 forbidden transitions. However, as pointed out by Ve rhoeve et al. in their far-infrared spectroscopic work [P. Verhoeve, M . Versluis, J. J. Ter Meulen, W. L. Meerts, and A. Dynamus. Chern. Phy s. Lett. 161, 195-201 (1989)], a near degeneracy exists between some ( J, 0)(+) and (J, 3)(-) ground state rotation-inversion levers, which c auses sizable shifts in these levels due to off-diagonal centrifugal d istortion. These shifts were observed in the ground state combination differences of the Ni fundamental transitions. We have observed 11 for bidden Delta\k - l\ = 3 transitions to the nu(3) band induced by the m ixing in the ground state and involving the J = 7, 9, and 11 levels, a nd determined the energy difference between different K levels, tile C rotational constant, and the off-diagonal centrifugal distortion mixi ng coefficient. (C) 1997 Academic Press.