ABSORPTION BY DISSOCIATIVE CONTINUA AND RYDBERG STATES IN CONDENSED MATTER - HCL IN RARE-GAS MATRICES

The absorption spectra of HCl in rare gas matrices have been recorded in the first continuum (A(1) Pi <-- X (1) Sigma(+)) region in Kr and X e matrices and up to 100 nm in Ar matrices. Concentration and temperat ure effects have been used to distinguish between absorption from mono mers and that from clusters. The first continuum band of the monomer i s seen to shift red by similar to 0.36 eV in Ar matrices, while it shi fts blue by similar to 0.3 and similar to 0.08 eV in Kr and Xe matrice s, respectively. Simultaneously, the oscillator strength of the A(1) P i state is seen to increase drastically in the sequence Ar-Kr-Xe. Thes e trends can be interpreted by the fact that the excited state is solv ated in Ar by dispersive and inductive interactions with the environme nts, while in Kr and Xe matrices, absorption is dominated by HCl-Rg(n) (+) charge transfer states (Rg = Kr, Xe). At higher energies and in Ar matrices, discrete absorption by the b(3) Pi, C-1 Pi, H-1 Sigma(+) K- 1 Pi and M(1) Pi states occurs and their relative intensities reproduc e well those of the gas phase. However, the b and C states are blue sh ifted with respect to their gas phase energies by similar to 0.6 eV, i n agreement with their predicted Rydberg character, while the H, K and M states are just slightly red shifted casting some doubt about their classification as Rydberg states.