Millimetre-wave and Fourier transform infrared spectra between 325 cm⁻¹and 4720 cm⁻¹of BrCN and global rovibrational analysis of the main isotopomers

Abstract

The infrared absorption spectrum of BrCN has been recorded in the region 325-4720cm-' with a Bruker 120 HR interferometer. More than 30 000 lines have been measured and most of them have been assigned: 10734 lines for 151 bands and 10993 lines for 150 bands of 79Br'2C'4N and "Br12Ci4N, respectively. Also new millimetre-wave spectra were measured for the vibrational excited states lying between 1000 cm-' and 1400 cm-' . After a band by band analysis of these transitions, rovibrational global analyses have been performed for both isotopomers using all available experimental data. The rotational I-type resonance and the anharmonic resonance associated with klz2 are taken into account in one-step diagonalization procedures. Sets of 73 molecular parameters are obtained for both isotopomers. It is shown that the existing equilibrium structure is likely to be reliable. The vibrational dependence of the quartic centrifugal distortion constant is analysed for the linear triatomic molecules studied so far.

Accuracy of the rotational constants

“…However, this calculation delivers equilibrium values whereas ground state values are needed. The difference was found to be of the order of 2% for linear triatomic molecules [27] but it can be much larger for asymmetric molecules [28]. Table 1 gives some typical values.…”

Ab initio anharmonic force field and equilibrium structure of vinyl fluoride and vinyl iodide

“…It is worth noting that the deviations are almost the same (in percentage) as for vinyl chloride [1]. It is likely that a large part of these deviations could be explained by the difference between ground state and equilibrium constants which values are known to be a few percent [33].…”

Equilibrium structure and force field of NH2

“…However, it has to be remembered that the calculated values are equilibrium values whereas the experimental values are ground state ones, the difference between the two kind of values being generally of the order of magnitude of 5%. 30 To check this point, the vibrational corrections to the equilibrium quartic centrifugal distortion constants has been calculated from the quartic force field by means of fourth-order perturbation theory. For this task, the computer program VIBROT 31 was used.…”