Infrared Absorption by Symmetrical NO3 Free Radical in the Gas Phase

A new infrared absorption band between 1325 and 1375 cm−1 has been observed in the N2O5–O3 system at low pressure in an 80-m path-length cell. In such systems the presence of the symmetrical NO3 free radical is well known in terms of its visible absorption spectrum, which varies in the unusual way of Kss[N2O5]13[O3]13. The new infrared band lies at a frequency just below that for the antisymmetric stretch of the symmetrical planar nitrate ion; the absorption optical density varies as [N2O5]13[O3]13; and the new absorption has been assigned to the symmetrical NO3 free radical.