RESUMEN
The spectrum of the nu(10) band of diborane, arising from the ring-puckering vibration, has been obtained with a spectral resolution of 0.0015 cm(-1) in the region 275-400 cm(-1). The spectrum of a sample enriched in (10)B was recorded as well as one with naturally abundant boron, i.e., 64% (11)B(2)H(6), 32% (10)B(11)BH(6), and 4% (10)B(2)H(6). This mode is the lowest vibrational level of the molecule and is unperturbed, allowing a complete assignment of not only the fundamental bands but also the 2nu(10)-nu(10) hot bands of all three boron isotopomers. The intensities of several hundred lines of the fundamental and hot bands of all isotopomers have been measured and vibrational transition moments have been obtained. Finally, it has been shown that the harmonic approximation does not apply for nu(10). Copyright 2000 Academic Press.
RESUMEN
Using high-resolution Fourier transform spectra, a thorough analysis of the nu14 c-type, nu17 a-type, and nu18 a-type bands of both 11B2H6 and 10B11BH6 has been carried in the 10.3-, 6.2-, and 8.5-µm spectral regions, respectively. From this analysis a large set of precise ground state combination differences with J values up to 36 (31) and Ka values extending to 18 (18) was derived for 11B2H6(10B11BH6). These data were fitted using a Watson-type Hamiltonian leading to accurate ground state rotational constants. An rs value for the B-B distance has been determined to be 1.7645(10) Å. The determination of upper state Hamiltonian constants proved to be much more difficult since the corresponding rotational levels of each of the bands are strongly perturbed by nearby dark states. To account for these strong localized resonances, it was necessary to introduce the relevant interacting terms in the Hamiltonian matrix. As a result it was possible to calculate the upper state energy levels quite satisfactorily. From these fits, estimates of the band centers and a few of the rotational constants of the resonating dark states were obtained. Copyright 1998 Academic Press.