Infrared diode-laser spectroscopy of the electronic ground state of GeD (X2Π1/2)

The spin-forbidden a 4Σ--X 2Π1/2 transition of GeH detected in absorption using intracavity laser spectroscopy

The a ⁴Σ^--X ²Π_1/2 transition of GeH has been recorded in absorption for the first time using Intracavity Laser Spectroscopy (ILS). The GeH molecules were produced in a 0.40-0.60 A DC plasma discharge inside an aluminum hollow cathode, using 500 mTorr of Ar, 100 mTorr of H₂, and 200 mTorr of GeH₄. This cathode is located within the resonator cavity of a Coherent Verdi™ V-10 pumped dye laser. Effective path lengths for this series of measurements using the ILS method ranged from 2 to 7 km. Spectra were calibrated using the absorption spectrum of I₂ collected from an extracavity cell, the I₂ transmission spectrum from Salami and Ross, J. Mol. Spectrosc. 223(1), 157 (2005) and PGOPHER's [C. M. Western, J. Quant. Spectrosc. Radiat. Transfer 186, 221-242 (2016)] calibration feature. Differences in peak positions between calibrated experimental spectra and the reference data were on average less than ±0.002 cm^-1. All eight branches expected to have appreciable intensity for the transition have been identified, and isotopologue splitting was observed in features of 5 of the 8 identified rotational branches. Molecular constants have been obtained for the a ⁴Σ^- states of ⁷⁰GeH (20.84% abundant), ⁷²GeH (27.54% abundant), and ⁷⁴GeH (36.28% abundant). The transitions were fit using PGOPHER, holding the ground state constants fixed to the values reported by Towle and Brown [Mol. Phys. 78(2), 249 (1993)]. The constants for the a ⁴Σ^- state of ⁷⁴GeH determined by the fit are T₀ = 16 751.5524(13) cm^-1, B₀ = 6.764 912(33) cm^-1, D₀ = 0.459 60(17) × 10^-3 cm^-1, λ_SS = 9.7453(12) cm^-1, λ_D = 0.468(14) × 10^-3 cm^-1, γ = 0.077 878(84), and γ_S = -0.361(77) × 10^-3 cm^-1.

The ground state energy levels and molecular structure of jet-cooled HGeCl and DGeCl from single vibronic level emission spectroscopy

Single vibronic level dispersed fluorescence spectra of jet-cooled HGeCl and DGeCl have been recorded by laser excitation of selected bands of the A 1A"-X 1A' electronic transition. Twenty-six ground state vibrational levels of HGeCl and 42 of DGeCl were measured, assigned, and fitted to standard anharmonicity expressions, which allowed all the harmonic frequencies to be determined for both isotopomers. A normal coordinate least squares analysis obtained by fitting the harmonic frequencies yielded reliable values for five of the six force constants. The ground state effective rotational constants and force field data were combined to calculate average (rz) and approximate equilibrium (re z) structures, with re z(GeH)=1.586(1) A, re z(GeCl)=2.171(2) A, and the bond angle fixed at our CCSD(T)/aug-cc-pVTZ ab initio value of 93.9 degrees . Comparisons show that the derived bond lengths are consistent with those of the appropriate diatomic molecules in their ground electronic states and the bond angle is similar to that of germylene (GeH2). A Franck-Condon simulation of the vibrational intensities in the 0(0) (0) band emission spectrum of HGeCl using ab initio force field data shows good agreement with experiment, lending credence to the vibrational analysis of the observed spectra.