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

Abstract

The 2ν4 band spectrum of 14NO3 observed with infrared diode laser spectroscopy was analyzed with the Fourier transform (FT) spectrum in the 760cm−1 region, including the Coriolis interaction between v4=2 and v2=1. The vibrational frequencies of v4=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 2ν4, ν3, ν4, ν2, and ν2+3ν4 states, a relation among the cubic anharmonic constants was obtained as 0.452 Φ444ζ2,4−0.271 Φ344ζ2,3=127.7cm−1. The ratio of transition moments μ(ν2)/μ(2ν4) was determined to be 0.3 from the perturbation analysis. The second strongest infrared band of 14NO3, ν3+2ν4, observed around 1927cm−1has been analyzed with the hot band ν3+2ν4−ν4 by including the Coriolis interaction with the v2=1, v4=3 state. Similarly, the same band of 15NO3 was analyzed to give the band origin of 1897.9325(6)cm−1. The isotope shift 28.2cm−1 for the ν3+2ν4 vibrational frequency is consistent with a predicted value of 27.3cm−1. Although there are two A′ states in v3=1, v4=2, only one A2′ state has been assigned in the hot band, indicating that the other band has weak intensity. This fact and the strong intensity of the ν3+2ν4 band (l3=±1, l4=0) are understood as the effect of vibronic interaction. The first-order Coriolis coupling constant ζ of ν3+2ν4, l3=1, l4=0 is similar to those of the ν4 and ν3+ν4 states, and it is concluded that the vibrational Coriolis coupling constant is nearly zero and the observed constants of ζ=−0.19 (14NO3) and ζ=−0.15 (15NO3) also originate from the effect of vibronic interaction.