The photodissociation dynamics of nitric acid studied at 193 nm by LIF and REMPI–TOF methods

The 193 nm photodissociation of HNO3 in a supersonic jet has been investigated by LIF and REMPI–TOF techniques probing the OH(X2Π) and the O(3P) products, respectively. The measured rotational state distribution of OH is shown to be dominated by a bimodal distribution consistent with the previously reported bimodal translational energy distribution of OH. An additional decay channel, yielding O(3P) fragments with high kinetic energy, has been observed and tentatively assigned to HNO3+hν → O(3P)+HONO(X̃1A′). Energetic considerations indicate that about one third of the HONO products are unstable, decaying further to OH + NO.