Multireference configuration interaction study of ground and low-lying excited states of the AlC radical

This work explored the spectroscopic parameters and vibrational properties of the 21 -S and 42 states of the AlC radical. The PECs were calculated with the CASSCF method, which was followed by the icMRCI+Q approach. The A(4), a(2), 5(2), 2(2), and 1(2)phi states as well as the first well of B-4 sigma(-) state were inverted with the spin-orbit coupling (SOC) effect included; the 1(4), 1(4)sigma(+), and 2(2)sigma(-) states as well as the second wells of the B-4 sigma(-), 2(2)sigma(+), 3(2)sigma(+), 4(2) and 5(2) states were weakly bound, which well depths were less than 650 cm(-1); the B-4 sigma(-), 2(2)sigma(+), 3(2)sigma(+), 4(2), 5(2), and 2(2) states had double wells and the second wells of these states except for B-4 sigma(-) had only several vibrational states; the avoided crossings existed between the 2(2)sigma(+) and 3(2)sigma(+) states, the 3(2)sigma(+) and 4(2)sigma(+) states, the B-4 sigma(-) and 3(4)sigma(-) states, the 2(2) and 3(2) states, the 4(2) and 5(2) states, the 5(2) and 6(2) states, as well as the 2(4) and 3(4) states. The extrapolation scheme, core-valence correlation and scalar relativistic corrections were included. The spectroscopic parameters and vibrational properties were determined. The TDM curves between two different -S states were calculated and Franck-Condon factors of some transitions were evaluated. The SOC effect on the spectroscopic and vibrational properties was evaluated.