Laser spectroscopy and dynamics of the jet-cooled AsH2 free radical

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

The òA₁-X̃²B₁ 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 2₁ ⁰, 0₀ ⁰, and 2₀ 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 r₀ ^″ = 1.724(2) Å, θ₀ ^″ = 90.38(7)° and r₀ ^' = 1.693(6) Å, θ₀ ^' = 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.

THE STUDY OF THE PROPERTIES OF THE GROUND- AND LOW-LYING EXCITED STATES OF ASH2, ${\rm ASH}_{2}^{+}$ AND ${\rm ASH}_{2}^{-}$

The properties of the ground and excited states of AsH2 , [Formula: see text] and [Formula: see text] have been investigated by using symmetry-adapted-cluster (SAC)/symmetry-adapted-cluster configuration interaction (SAC-CI) method. The geometry of the ground state of AsH2 is optimized at SAC method with different basis sets. The calculated results with cc-pVTZ and cc-pVQZ basis sets are in very good agreement with the experimental and previous theoretical data. The geometry and the properties of eight low-lying electronic excited states of AsH2 are obtained at SAC-CI/cc-pVTZ and SAC-CI/cc-pVQZ level, including geometries, vertical excitation energies, adiabatic excitation energies, transition dipole moments, and oscillation strengths. Employing the same theoretical level as AsH2 , the geometries, adiabatic ionization potentials (AIPs), and vertical ionization potentials (VIPs) of the ground and eight low-lying electronic states of [Formula: see text] are investigated as well as the geometries, vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) of nine electronic states of [Formula: see text]. Comparing with the available experimental or previous theoretical data, the SAC/SAC-CI/cc-pVTZ and SAC/SAC-CI/cc-pVQZ results are reliable for AsH2 , [Formula: see text] and [Formula: see text]. The predicted results can afford the useful information for one to deeply investigate them from the spectral experiment.

AB INITIOSTUDY OF SPECTROSCOPIC CONSTANTS AND ANHARMONIC FORCE FIELD OFAsH2RADICAL

The equilibrium structure, spectroscopic constants and anharmonic force field of AsH2have been investigated at B3LYP, B3PW91 and MP2 methods employing the basis sets of cc-pVNZ and aug-cc-pVNZ (N ∈ { T , Q }), respectively. The computed geometries, rotational constants, part of vibrational frequencies, quartic and sextic centrifugal distortion constants are compared with the available experimental data or theoretical results. The other vibrational frequencies, equilibrium rotational constants, anharmonic constants, vibration–rotation interaction constants, cubic and quartic force constants of AsH2are also predicted for the first time. Furthermore, the calculated results show that the DFT method is superior to MP2 at the calculations of geometries, spectroscopic constants and force constants. The B3PW91/aug-cc-pVQZ results are more reliable. Our predictions can provide useful data for the experimental studies of the corresponding spectroscopic constants of AsH2.