Fourier transform infrared spectroscopy of BH3 with the first identification of the ν4 band

Abstract High-resolution Fourier transform infrared spectra of the ν4 bands of 11BH3 and 10BH3 have been analyzed by taking into account Coriolis interaction between the v4=1 and v2=1 states in the 900-1300 cm-1 region. The main parameters thus obtained are the band origin ν4=1196.022(1), the rotational constant B4=7.9759(2), C4=3.84033(9), the first-order Coriolis coupling constant Cζ4=-0.3255(2), the Coriolis interaction constant D24(∼(2)1/2Bζ24)=7.7065(3) cm-1 for 11BH3, and ν4=1201.805(7) B4=7.9662(7), C4=3.8466(3), Cζ4=-0.3282(8), D24=7.631(1) cm-1 for 10BH3 with one standard deviation in parentheses. The ν2 band of 10BH was analyzed for the first time to determine ν2=1159.409(2), B2=7.8259(8), C2=3.8887(2) cm-1 and other constants. The observed absorption line intensities of the ν4 and ν2 bands were explained by using the ratio of the transition moments μ4/μ2=0.4. Assignments in the ν3 bands of 11BH3 and 10BH3 were extended with a set of newly determined ground state constants.