Caesium hydride: MS-CASPT2 potential energy curves and AΣ→XΣ absorption/emission spectroscopy.

Correlated ab initio methods (CASPT2 and CCSD(T)) in conjunction with the ANO-RCC basis sets were used to calculate potential energy curves (PECs) of the ground, valence, and Rydberg electronic states of CsH with the inclusion of the scalar relativistic effects. The spectroscopic constants of bound states were calculated from the PECs and compared with previous theoretical and/or available experimental data. Absorption and emission spectra arising from the transition between XΣ and AΣ states were modelled using vibrational and rotational energy levels and corresponding nuclear wave functions obtained via the direct numerical integration of one-dimensional rovibrational Schrödinger equation in the CASPT2/ANO-RCC electronic potentials. The anharmonic shape of the AΣ potential and the shape of the pertinent vibrational wave functions have an interesting impact on the final shape of the spectrum and result in the complicated fine structure of individual emission bands.