Observation of two Ω=0+ excited electronic states in jet-cooled LaH

Abstract

Lanthanum hydride (\chem{LaH}) molecules were produced in a pulsed supersonic molecular beam by reaction of laser produced lanthanum metal plasma with $\sim$2\% ammonia seeded in helium gas. Rotationally resolved laser-induced fluorescence excitation bands involving two excited electronic states, originating from $\nu$=0 of ground state \textit{X}$^{1}$$\Sigma$$^{+}$ were observed with band origins at 21970.71(1) and 22100.31(3) cm$^{-1}$. Rotational analysis confirmed these transitions as \textit{$\Omega$}=0$^{+}$- \textit{X}$^{1}$$\Sigma$$^{+}$. The rotational lines up to J$^{"}$=6 were observed in the 21970.71 cm$^{-1}$ band. However, for the 22100.31 cm$^{-1}$ band, rotational lines up to J$^{"}$=12 in the P-branch and J$^{"}$up to 10 in the R-branch was observed. The molecular constants for both the excited states were determined by fitting rotational line wavenumbers to an effective Hamiltonian operator for \textit{$\Omega$}=0$^{+}$ and \textit{X}$^{1}$$\Sigma$$^{+}$ state using the Pgopher program.