# High-level ab initio calculations on HGeCl and the equilibrium geometry of the A1A'' state derived from Franck-Condon analysis of the single-vibronic-level emission spectra of HGeCl and DGeCl

Daniel K W Mok, Foo-Tim Chau, Edmond P F Lee, John M Dyke

*Journal of Computational Chemistry 2010, 31 (3): 476-91*

19499544

CCSD(T) and/or CASSCF/MRCI calculations have been carried out on the X(1)A' and A(1)A'' states of HGeCl. The fully relativistic effective core potential, ECP10MDF, and associated standard valence basis sets of up to the aug-cc-pV5Z quality were employed for Ge. Contributions from core correlation and extrapolation to the complete basis set limit were included in determining the computed equilibrium geometrical parameters and relative electronic energy of these two states of HGeCl. Based on the currently, most systematic CCSD(T) calculations performed in this study, the best theoretical geometrical parameters of the X(1)A' state are r(e)(HGe) = 1.580 +/- 0.001 A, theta(e) = 93.88 +/- 0.01 degrees and r(e)(GeCl) = 2.170 +/- 0.001 A. In addition, Franck-Condon factors including allowance for anharmonicity and Duschinsky rotation between these two states of HGeCl and DGeCl were calculated employing CCSD(T) and CASSCF/MRCI potential energy functions, and were used to simulate A(1)A'' --> X(1)A' SVL emission spectra of HGeCl and DGeCl. The iterative Franck-Condon analysis (IFCA) procedure was carried out to determine the equilibrium geometrical parameters of the A(1)A'' state of HGeCl by matching the simulated, and available experimental SVL emission spectra of HGeCl and DGeCl of Tackett et al., J Chem Phys 2006, 124, 124320, using the available, estimated experimental equilibrium (r(e)(z)) structure for the X(1)A' state, while varying the equilibrium geometrical parameters of the A(1)A'' state systematically. Employing the derived IFCA geometry of r(e)(HGe) = 1.590 A, r(e)(GeCl) = 2.155 A and theta(e)(HGeCl) = 112.7 degrees for the A(1)A'' state of HGeCl in the spectral simulation, the simulated absorption and SVL emission spectra of HGeCl and DGeCl agree very well with the available experimental LIF and SVL emission spectra, respectively.

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