A CASPT2 study of the spectral shift of the resonance emission lines of Rb and Cs embedded in liquid He

Highlights: • A simple cluster model to evaluate the spectral shift in the emission spectra of alkali probes in liquid He. • Calculated emission takes into consideration the cavity increase after excitation. • The shift in the s ← p emission is obtained with CASPT2 calculation. The emission line shifts of the resonance transitions (s ← p) of Rb and Cs embedded in liquid He environment have been estimated using CASPT2 with quadruple-zeta basis sets. The liquid He environment has been approximated by a spherically symmetric model cluster, with 14 He atoms placed in equidistant positions from the central alkali atom. The emission line for the D1 transition is found to be blue shifted. The shift is estimated to be −1.2 to −1.8 nm for Rb and −2.2 to −2.6 nm for Cs, in very good agreement with the experimental estimates of −1.2 nm and −2.1 nm respectively obtained in liquid He.