Rovibrational spectra of LiH₂⁺, LiHD⁺ and LiD₂⁺ determined from FCI property surfaces

Full configuration interaction (FCI) has been used in conjunction with the lithium [6s5p3d1f] (Iron, M. A.; et al. Mol. Phys. 2004, 101, 1345) and hydrogen aug-cc-pVTZ basis sets to construct an 83-point potential energy surface of the ¹A₁ ground state of ⁷LiH₂⁺. Vibrational and rovibrational wave functions of the⁶,⁷LiH₂⁺, ⁶,⁷LiHD⁺, and ⁶,⁷LiD₂⁺ ground states were calculated variationally using an Eckart−Watson Hamiltonian. For 7LiD₂⁺, rovibrational transition frequencies for K = 0, 1, 2 and J ≤ 10 are within ca. 0.1% of recent experimental values (Thompson, C. D.; et al. J. Chem. Phys. 2006, 125, 044310). A 47-point FCI dipole moment surface was embedded in the rovibrational Hamiltonian to calculate vibrational and rovibrational radiative properties. At 296 K, with v ≤ 4 and J ≤ 4, the 20₂ ← 303 rotational transition in the |001> band was found to have the greatest spectral intensity with respect to the ground electronic states of ⁶,⁷LiH₂⁺, ⁶,⁷LiHD⁺, and ⁶,⁷LiD₂⁺. In each case, the most intense rovibrational transitions have been assigned unequivocally using the J, Ka, Kc assignment scheme