Infrared laser spectroscopy of the ν3-ν4 difference band and detection of the ν3 band of NO3

Highlights: • Infrared diode laser spectroscopy of the ν₃-ν₄ difference band of ¹⁴NO₃ is reported. • The weak ν₃ fundamenta band of NO₃ has been detected for the first time. • The absorption intensity of the ν₃ band was ~ 1/2000 of the strongest ν₃ + ν₄ band. • The very small Coriolis coupling constant in v₃ = 1 was explained by vibronic interaction. The infrared diode laser spectrum of the ν₃-ν₄ difference band of ¹⁴NO₃ has been observed in the 690 cm⁻¹ region. By fixing the lower state (v₄ = 1) constants to the previously determined values, molecular constants in v₃ = 1 have been determined for the first time : the vibrational energy E₃ = 1054.13679(69) cm⁻¹, the rotational constants B₃ = 0.4562291(41), C₃ = 0.2274567(53) cm⁻¹, the first-order Coriolis coupling constant Cζ₃ = 0.0032073(99) cm⁻¹, and the spin–orbit interaction constant a_eff = –0.03979(70) cm⁻¹, with one standard deviation in parentheses. The ν₃ fundamental band has been detected with weaker intensity than the ν₃ + ν₄ band by a factor of ~ 2000.