Fourier Transform Infrared Spectrum of FCN: The 1800–2800 cm−1Spectral Range

FT Infrared Spectra of FCN from 1200 to 1800 cm−1 and from 2800 to 7000 cm−1 and Global Rovibrational Analysis of the Main Isotopomers

“…In the case of the avoided crossing between 30 0 0 and 02 0 1 states, we so calculate the direct coupling term as 0.031 cm Ϫ1 , whereas the effective interaction energy is estimated to be about 4 cm Ϫ1 (14). This confirms that the interaction essentially results from the indirect coupling through the first-order anharmonic resonances associated with k 122 and k 113 .…”

“…On the contrary, the anharmonic interactions connect rather far away states, so that their effect is mainly on E v and B parameters and with very small contributions to higher order terms. One exception occurs in the case of 3 1 and 2 2 ϩ 3 states which are very close to each other (14) with an avoided crossing near J ϭ 47. The corresponding infrared bands require a fourth-order L parameter, but nevertheless the fit is not perfect, with systematic residuals approaching Ϯ0.001 cm Ϫ1 .…”

“…Although the experimental data available for those two isotopic varieties is quite scarcer than for the main species and those data cover a smaller range in J and in the v i 's, it is possible to apply to them our global rovibrational analysis. We indeed expect that the molecular parameters will change by a few percent (up to about 10% for some of them) with the change of mass from 12 C to 13 C or from 14 N to 15 N. The highest order parameters of which the contribution to the energy is marginal can be fixed to their value for the main isotopomer. On the contrary, the lowest order parameters are left completely free and are well determined from the experimental data.…”

“…(14). The available microwave and millimeter-wave frequencies in the lower vibrational state of the transition were used with the infrared wavenumbers.…”

“…They concern all vibrational states up to 2400 cm Ϫ1 , and they add 122 accurate measurements to the 46 previous experimental data. The first part of the infrared study (14) covered the 1800 -2800 cm Ϫ1 domain: in addition to the five bands previously reported by Lafferty (5), 45 bands of 19 In the present paper, we present the results of infrared measurements in the regions from 1200 to 1800 cm Ϫ1 and from 2800 to 7000 cm Ϫ1 . Some details given in the previous paper (14) about the spectra and their analysis are not repeated here.…”