Absorption by dissociative continua and Rydberg states in condensed matter: HCl in rare gas matrices Original Research Article

The absorption spectra of HCl in rare gas matrices have been recorded in the first continuum (A1∏ ← X1Σ+) region in Kr and Xe matrices and up to 100 nm in Ar matrices. Concentration and temperature effects have been used to distinguish between absorption from monomers and that from clusters. The first continuum band of the monomer is seen to shift red by ∼ 0.36 eV in Ar matrices, while it shifts blue by ∼ 0.3 and ∼ 0.08 eV in Kr and Xe matrices, respectively. Simultaneously, the oscillator strength of the A1∏ state is seen to increase drastically in the sequence. ArKrXe. These trends can be interpreted by the fact that the excited state is solvated in Ar by dispersive and inductive interactions with the environments, while in Kr and Xe matrices, absorption is dominated by HCl−-Rgn+ charge transfer states (Rg Kr, Xe). At higher energies and in Ar matrices, discrete absorption by the b3∏, C1∏, H1Σ+, K1∏ and M1∏ states occurs and their relative intensities reproduce well those of the gas phase. However, the b and C states are blue shifted with respect to their gas phase energies by ∼ 0.6 eV, in 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.