On the C(1)Sigma(+) State of LaH

Theoretical calculation of the low-lying electronic states of the LaH molecule

The potential energy curves of the low-lying electronic states of the LaH molecule are reported via the CASSCF method with multireference calculations (single and double excitations with Davidson corrections). Twenty-four low-lying electronic states of the LaH molecule in the representation 2s+1Λ(+/−) below 20 000 cm−1 were investigated along with five lower electronic states in the Ω representation. The harmonic frequency ωe, the equilibrium internuclear distance Re, the rotational constants Be, and the electronic energy with respect to the ground state Te were calculated for these states. Twelve new electronic states are investigated in the present work for the first time that have not yet been observed experimentally. Using the canonical functions approach, the eigenvalues Ev, the rotational constants Bv, the centrifugal distortion constants Dv, and the abscissas of the turning points Rmin and Rmax were calculated for the investigated electronic states up to vibrational level v = 43.

Energy linkage between the singlet and triplet manifolds in LaH, and observation of new low-energy states

Wavelength-resolved fluorescence spectra of jet-cooled LaH were obtained from D1, E1, and 0(+)((3)Σ(-)) states by exciting isolated rotational levels. The observation of a(3)Δ(1) and a(3)Δ(2) states at 1259.5(5) and 1646(1) cm(-1), respectively, established the missing energy link between the singlet and triplet manifolds. The low-energy b(3)Π(0,1) and B(1)Δ(2) states predicted earlier from ab initio studies were also observed for the first time. Vibrational constants ω(e) = 1418(2) cm(-1), ω(e)x(e) = 15.6(7) cm(-1) for the ground and ΔG(1∕2) = 1326.1(7) and 1312(1) cm(-1), respectively, for the a(3)Δ(1) and b(3)Π(1) states were also determined. Vibrational frequencies were found to be in excellent agreement with earlier ab initio values. However, ab initio term energies and spin-orbit separation of (3)Δ(2)-(3)Δ(1) and (3)Π(1)-(3)Π(0) were found to be in poor agreement with the present observations. Also, the (3)Π state that was predicted to be inverted is observed to be regular.