Vibronic Level Density of Excited NO2‐States and its Statistical Analysis

Measurements of vibronic term values in excited electronic states of NO2 have been performed with cw dye lasers over the whole spectral range from 12117 cm−1 to 24563 cm−1. The low rotational temperatures, achieved by adiabatic cooling of NO2 seeded in a supersonic argon beam, allow the separation of closely lying bands as well as a distinction between transitions to the 2B1 state and the vibronically coupled 2B2 – 2A1 states. The statistical analysis of the distribution P(S), where S is the energy separation between adjacent vibronic levels and of the intensity distribution of all measured bands, suggests that a short range correlation exists between the excited levels. Whether also a long range correlation exists is still under investigation. A definite answer requires an unambiguous determination of all bands even with low intensities and a safe assignment of all hot bands. These points are discussed in detail.