The Coriolis Interaction between the v2 = 1 and v3 = 2 States of Nitrosyl Bromide: Anomalous Quadrupole Patterns and Interstate Transitions in the Millimeter-Wave Spectrum.
The millimeter-wave rotational spectra of 79BrNO and 81BrNO in the v2 = 1 and v3 = 2 vibrational states have been reinvestigated. Measurements of the rotational spectrum in the region of maximum c-type Coriolis interaction between the two states allowed the previous analysis to be extended to account for some uncommon effects. For the most perturbed transitions the nuclear quadrupole hyperfine structure arises from coupling of not only the bromine nucleus, but also the nitrogen nucleus with the rotational angular momentum. These effects were satisfactorily fitted with a Hamiltonian describing Coriolis coupling in a molecule with two quadrupolar nuclei. The successful analysis of pure rotational transitions then allowed accurate prediction of rovibrational transitions, six of which were measured for 79BrNO and four for 81BrNO. Copyright 1998 Academic Press.
The prediction of spectroscopic properties from the quartic force field of NOBr
Abstract Ab initio molecular electronic structure methods are used to determine the constants describing the infrared spectroscopy of NOBr. Second-order Moller-Plesset perturbation theory (MP2) with a 6311G extended basis set on bromine is used to obtain an equilibrium geometry, harmonic vibrational frequencies and a quartic expansion of the potential energy surface. The cubic and quartic force constants were evaluated in mass-weighted normal coordinates using a finite-difference approach. Standard perturbation theory is then used to determine effective vibrational and rotational Hamiltonians for the fundamental vibrations and selected overtone and combination bands. The quadratic and most of the cubic potential constants are also determined experimentally. The calculated anharmonic constants are found to be in excellent agreement with experiment if a MP2 potential is used.
A high resolution far infrared study of rotation in HN3, HNCO, HNCS, and their deuterium derivatives
Abstract The pure rotational spectra of HN3, HNCO, HNCS and their deuterium derivatives have been obtained in the spectral range 20–250 cm−1 with spectral slit widths of 0.2–0.5 cm−1. Both the widely spaced RQK branches (ΔK = + 1) and their associated RRK and RPK branches were observed. For HN3 the Q branches can be fitted reasonably well by first-order distortion theory, but higher-order treatment is required for HNCO and HNCS because of the unprecedentedly large centrifugal distortion. Analysis of the data yields the following values of the rotational constants A 0 - B 0 , B 0 and DK respectively, all in cm−1; HN3, 19.94 ± 0.03, 0.3967 ± 0.0002, (0.766 ± 0.002) × 10−2; HNCO, 30.22 ± 0.1, 0.3664 ± 0.0002, 0.17 ± 0.01; HNCS, 44.70 ± 0.1, 0.1950 ± 0.001, 1.20 ± 0.1. The very large values of DK for HNCO and HNCS have significance only when taken along with terms involving K up to K10.