High-Resolution Infrared Spectrum of BrCN in the ν2 and ν1/2ν2 Regions

FT infrared spectra of BrCN have been recorded in the region of the ν2 band near 340 cm−1, the ν1 band near 580 cm−1, and the 2ν2 band near 690 cm−1 with a resolution between 2.9 and 4.7 × 10−3 cm−1. The vibrational levels (0110), (1000), (0200), (0220), (1110), and (2000) have been analyzed employing cold bands, hot bands, and new millimeter-wave transitions. Band-by-band polynomial analyses and a combined fit of all data relevant to the 2v1 + v2 = 2 polyad levels have been performed. The latter fit considered l-resonance interactions between the (0200), e and (0220), e levels and Fermi resonance between the two Σ states (1000) and (0200). Altogether about 1000 pieces of data up to J = 100 were fitted for each of the two isotopic species with rms of the residuals of 2–8 × 10−4 cm−1 for the infrared and 10–120 kHz for the pure rotational data.