The 1650-1350 Å absorption spectrum of nitrogen dioxide

An analysis of the 1650-1350 Å band system of nitrogen dioxide has been carried out. A pattern of band spacings and intensities is found that is complex but regular. It is shown that this pattern is qualitatively, and to a large extent quantitatively, just what would be expected for a transition in which the shape of the molecule changes from bent to linear. The transition is a parallel one and the upper state has 2Σ+u symmetry. The symmetrical stretching frequency is increased from its ground-state value to ca. 1420 cm-1 in the upper state. The upper-state bending frequency is ca. 600 cm-1. The N — O length is decreased from its groundstate value, probably to 1·1(3) Å. The upper state resembles closely the ground state of NO+2. The transition is to be classed as one of the Rydberg transitions leading to the first ionization potential of NO2; and the orbital to which the odd electron is transferred in the transition is (pσ) in type. The anharmonic constant g22 for the linear upper state is found to be 2·(3) cm-1. Other Rydberg transitions may well be present in the region, but have not been definitely identified.