FLUORESCENCE-DIP INFRARED-SPECTROSCOPY OF TROPOLONE AND TROPOLONE-OD

Fluorescence-dip infrared spectroscopy (FDIRS) is employed to record t he infrared spectra of the isolated, jet-cooled tropolone molecule (Tr OH) and its singly deuterated isotopomer TrOD in the O-H and C-H stret ch regions. The ability of the method to monitor a single ground-state level enables the acquisition of spectra out of the lower and upper l evels of the zero-point tunneling doublet free from interference from one another. The high power of the optical parametric oscillator used for infrared generation produces FDIR spectra with good signal-to-nois e despite. the weak intensity of the C-H and O-H stretch transitions i n tropolone. The expectation that both spectra will exhibit two OH str etch transitions separated by the OH(upsilon = 1) tunneling splitting is only partially verified in the present study. The spectra of TrOH a re compared with those from deuterated tropolone (TrOD) to assign tran sitions due to C-H and O-H, which are in close proximity in TrOH. The appearance of the spectra out of lower (a(1) symmetry) and upper (b(2) symmetry) tunneling levels are surprisingly similar. Two sharp transi tions at 3134.9 cm(-1) (out of the a(1) tunneling level) and 3133.9 cm (-1) (out of the b(2) tunneling level) are separated by the ground-sta te tunneling splitting (0.99 cm(-1)), and thereby terminate in the sam e upper state tunneling level. Their similar intensities relative to t he C-H stretch transitions indicate that the gamma- and z-polarized tr ansitions are of comparable intensity, as predicted by ab initio calcu lations. The corresponding transitions to the other member of the uppe r state tunneling doublet are not clearly assigned by the present stud y, but the broad absorptions centered about 12 cm(-1) below the assign ed transitions are suggested as the most likely possibility for the mi ssing transitions. (C) 1996 American Institute of Physics.