A Theoretical Description of the Photodissociation Spectrum of the H2O...HCl Complex

The effect of association of the water molecule and hydrogen chloride on the UV absorption bands is studied. Complete ab initio calculations for the H2O...HCl complex in the S1 and S2 states are performed. A mathematical model using Airy functions is developed to describe the absorption cross-sections in a continuous spectrum. The form of the potential is determined by accurate ab initio calculations. The cross-sections of potential surfaces of lower electron states are found from ab initio calculations using the Hartree–Fock, configurational interaction, and multi-configurational interaction techniques. A complete vibrational analysis and an analysis of the change in the electron density for the S0 → S1 transition on moving along the reaction coordinate allow a conclusion to be made on the feasibility of applying the model proposed to the H2O...HCl complex. The results obtained in the framework of the model using Airy functions show reasonably good agreement with the experiment. For the H2O...HCl heterodimer, the absorption band has the same structureless form as for the water monomer. The absorption band (peaking at λ ∼ 161 nm) is seen to shift towards short wavelengths as compared with the water monomer H2O (λ ∼ 167 nm).