Two-photon ionization spectroscopy and all-electron ab initio study of LiCa

Resonant two-photon ionization spectra of LiCa have been obtained from a laser vaporization, supersonic expansion source. The ground state of the molecule is confirmed to be X 2?+. Three band systems have been observed near 15 282, 19 310, and 22 250 cm-1 and the upper states have been assigned as 2?+, 2IIr , and, tentatively, 2II. Bond lengths and vibrational frequencies are reported for 7Li40Ca for the various states as X 2?+: r0=3.3796(11) ?, D?1/2=195.2 cm21; 2?+: r0=3.4275(47) ?, D?1/2=283.5 cm-1; 2IIr : re=3.5451(36) ?, ve5144.5 cm-1; and 2II: ve 5178.53(5) cm21. The ionization energy was also measured to be 4.471(1) eV by observing the onset of one-photon ionization. Results of ab initio all-electron calculations on twelve low-lying states [2?+(1), 2?+(2), 2?+(3), 2?+(4), 4?-(1), 4?-(1), 2II(1), 2II(2), 2II(3), 2II(4), 4II(1), and 4II(2)] are also reported, along with results on the X 1?+ ground electronic state of LiCa1. The dissociation energies of LiCa(X 2?+) into Li(2S)1Ca(1S) and of LiCa1 (X 1?+) into Li1(1S)1Ca(1S) are calculated to be 0.24 and 1.20 eV respectively, and the vertical and adiabatic ionization energies of LiCa have been determined to be almost the same, 4.43 eV, at the quadratic configuration interaction, including singles and doubles with approximate triples and all correlated electrons [QCISD(T,FULL)] level of theory.