Infrared spectroscopy of 2ν4 and ν3 + 2ν4 bands of the NO3 radical

Abstract The 2ν 4 band spectrum of 14 NO 3 observed with infrared diode laser spectroscopy was analyzed with the Fourier transform (FT) spectrum in the 760 cm −1 region, including the Coriolis interaction between v 4 = 2 and v 2 = 1. The vibrational frequencies of v 4 = 2, l = 0, and l = ±2 have been determined to be 752.4033(86) and 771.7941(81) cm −1 , respectively. By considering the anharmonic interaction among the 2ν 4 , ν 3 , ν 4 , ν 2 , and ν 2 + 3ν 4 states, a relation among the cubic anharmonic constants was obtained as 0.452 Φ 444 ζ 2,4 − 0.271 Φ 344 ζ 2,3 = 127.7 cm −1 . The ratio of transition moments μ(ν 2 )/μ(2ν 4 ) was determined to be 0.3 from the perturbation analysis. The second strongest infrared band of 14 NO 3 , ν 3 + 2ν 4 , observed around 1927 cm −1 has been analyzed with the hot bandν 3 + 2ν 4 − ν 4 by including the Coriolis interaction with the v 2 = 1, v 4 = 3 state. Similarly, the same band of 15 NO 3 was analyzed to give the band origin of 1897.9325(6) cm −1 . The isotope shift28.2 cm −1 for the ν 3 + 2ν 4 vibrational frequency is consistent with a predicted value of 27.3 cm −1 . Although there are two A ′ states in v 3 = 1, v 4 = 2, only one A 2 ′ state has been assigned in the hot band, indicating that the other band has weak intensity. This fact and the strong intensity of the ν 3 + 2ν 4 band ( l 3 = ±1, l 4 = 0) are understood as the effect of vibronic interaction. The first-order Coriolis coupling constant ζ of ν 3 + 2ν 4 , l 3 = 1, l 4 = 0 is similar to those of the ν 4 and ν 3 + ν 4 states, and it is concluded that the vibrational Coriolis coupling constant is nearly zero and the observed constants of ζ = −0.19 ( 14 NO 3 ) and ζ = −0.15 ( 15 NO 3 ) also originate from the effect of vibronic interaction.