(H2SE)-SE-80 - HIGH-RESOLUTION STUDY OF THE 3-NU(2), NU(1)+NU(2), AND NU(2)+NU(3) BANDS AND DETERMINATION OF EQUILIBRIUM ROTATIONAL-CONSTANTS AND STRUCTURE

High resolution Fourier transform spectra of monoisotopic (H2Se)-Se-80 have been recorded with a resolution of 7 x 10(-3) cm(-1) in the 3200-3500 cm(-1) spectral domain where it is easy to observe the main absorbing bands nu(1), + nu(2) and nu(2) + nu(3). Because of the excellent signal-to-noise ratio, it was also possible to locate and assign the 3 nu 2 band which appears in the lower wavenumber range. The (030), (110), and (011) rotational levels were least-squares fitted using a Hamiltonian which takes explicitly into account the strong Coriolis interaction coupling the rotational levels of (110) and (011)as well as weak Fermi-type and Coriolis-type interactions between (030), and(110) and (011), respectively. In this way, it was possible to calculate all the experimental energy levels to within the experimental uncertainty and a precise set of vibrational energies and rotational and coupling constants was obtained for the three Vibrational states with the band centers nu(0)(3 nu 2)= 3076.9040, nu(0)(nu(1) + nu(2))= 3361.6964, and nu(0)(nu(2) + nu(3))= 3371.7935 cm(-1). These results combined with those of a number of other vibrational states have been used to obtain the equilibrium rotational constants and their first order corrections as well as the spectroscopic vibrational constants of the molecule. Finally, neglecting the electronic corrections, the equilibrium structure of (H2Se)-Se-80 was obtained as follows: r(e)(Se - H) = 1.459099 + 0.000077 Angstrom; measured angle(H Se H)(e) = 90 degrees.958 + 0.011. (C) 1994 Academic Press, Inc.