Spectroscopic characterization of the lowest singlet states of CdNe, CdAr, and CdKr

We report the characterization of the first excited singlet states of CdNe, CdAr, and CdKr, which correlate with Cd(5s5p 1P1) and the ground-state rare-gas atoms. The van der Waals molecules were created in a free jet supersonic expansion and studied by laser-induced fluorescence, dispersed fluorescence, laser pump/probe action spectra, and spectral simulations. The C 1Π1 states are found to be more strongly bound than their triplet counterparts: 116Cd20Ne (De=89 cm−1, ωe=23.36 cm−1, ωexe=1.80 cm−1, re =3.61±0.05 Å); 116Cd40Ar (De=544 cm−1, ωe=47.97 cm−1, ωexe=1.11 cm−1, re=3.28±0.05 Å); 114Cd84Kr (De=1036 cm−1, ωe=56.72 cm−1, ωexe=0.81 cm−1, Δre(C 1Π–X 1Σ+) =1.16 Å). This is attributed to spatial differences between the atomic p orbital of the singlet vs the triplet excited state of the Cd atom. The D 1Σ0+ states of CdAr and CdKr were found to be repulsive for Franck–Condon accessible internuclear distances. No production of Cd(5s5p 2PJ) states from predissociation of any C 1Π1 molecular state was observed.