Laser Spectroscopy Of The C2π (41242 Cm−1) And 2∆ (42192 Cm−1) States Of Magnesium Hydride

Two laser-induced fluorescence techniques were used to access the high-lying C$^{2}\Pi$ state (41242 \wn) in the metal-bearing molecule MgH. First, we directly excited the C$^{2}\Pi$ state from the X$^{2}\Sigma^{+}$ ground state with UV light produced by frequency-doubling pulsed visible laser light. Second, a resonant two-photon experiment was performed with different laser beams tuned to the A$^{2}\Pi$ - X$^{2}\Sigma^{+}$ and C$^{2}\Pi$ - A$^{2}\Pi$ transitions. Term energies for levels up to J = 11.5 were fit to a $^{2}\Pi$ Hamiltonian to yield rotational parameters B = 6.1045(10) \wn, D = 3.176(86)$\times10^{-4}$ \wn, A = 3.843(60) \wn, and p = -2.653(88) $\times10^{-2}$ \wn. We also observed levels of a $^{2}\Delta$ state (42192 \wn) up to J = 4.5 with the two-photon technique. Guntch previously observed the $^{2}\Delta$ - A$^{2}\Pi$ spectrum in 1937, but assigned the upper state as $^{2}\Sigma^{-}$. The molecular parameters determined for the $^{2}\Delta$ state are B = 6.2861(23) \wn and A = -0.168(17) \wn