The electronic spectrum of the jet-cooled stibino (SbH2) free radical.

The A ̃ 2 A 1 − X ̃ 2 B 1 electronic transition of the jet-cooled stibino (SbH2 and SbD2) free radical has been observed for the first time using laser induced fluorescence (LIF) detection. The radicals were produced by a pulsed electric discharge through a mixture of stibine (SbH3 or SbD3) in high pressure argon at the exit of a pulsed molecular beam valve. SbH2 exhibits only three LIF bands, assigned as 2 1 0 , 0 0 0 , and 2 0 1 , with a fluorescence lifetime (τ), which decreases from ∼50 ns for 00 to <10 ns for 21. LIF transitions to the 00 (τ ∼ 2 µs), 21 (τ ∼ 400 ns), and 22 (τ ∼ 75 ns) upper vibronic states of SbD2 were also observed. High-resolution spectra exhibited large spin-rotation splittings and small resolved antimony hyperfine splittings due to a substantial Fermi contact interaction in the excited state. The experimentally determined rotational constants gave effective molecular structures of r 0 ″ = 1.724(2) Å, θ 0 ″ = 90.38(7)° and r 0 ′ = 1.693(6) Å, θ 0 ′ = 120.6(3)°. The ground state bending vibrational levels up to eight quanta (6404 cm−1) in SbH2 and 12 quanta (6853 cm−1) in SbD2 were measured from dispersed fluorescence spectra. All indications are that SbH2 undergoes a dissociative process at low vibrational energies in the excited electronic state. [ABSTRACT FROM AUTHOR]