The ν₃ Fundamental in NO₃ Has Been Seen Near 1060 cm^–1, Albeit Some Time Ago

A high-quality vibronic Hamiltonian, recently constructed for the X̃²A′₂ and B̃²E′ interacting electronic states in the NO₃ radical, has been used to simulate the negative ion photodetachment spectrum of NO₃^–. The simulation is in striking agreement with experiment; band positions are accurate to within a few tens of cm^–1, and relative intensities are also faithfully reproduced. This allows for some additional insight into the spectroscopy of NO₃ and the quite unambiguous assignment of some of the features in the negative ion photodetachment spectrum. Most significant is the finding that the feature ca. 1060 cm^–1 above the origin contains a sizable contribution that can be assigned to a transition from the anion ground state to the ν₃ level in NO₃; the nearby ν₁ level is unresolvable at the experimental resolution. Thus, the work of Weaver et al. appears to provide an experimentally determined position for this elusive and rather controversial vibrational state of NO₃.