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Ab Initio Calculations and Franck–Condon Simulation of the Absorption Spectra of GeCl 2 Including Anharmonicity
Author(s) -
Mok Daniel K. W.,
Chau Footim,
Lee Edmond P. F.,
Dyke John M.
Publication year - 2005
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200400489
Subject(s) - anharmonicity , chemistry , atomic physics , absorption spectroscopy , ab initio , ab initio quantum chemistry methods , spectral line , absorption (acoustics) , molecular physics , physics , molecule , organic chemistry , quantum mechanics , astronomy , acoustics
Geometrical parameters, vibrational frequencies and relative electronic energies of the X̃ 1 A 1 , ã 3 B 1 and à 1 B 1 states of GeCl 2 have been calculated at the CCSD(T) and/or CASSCF/MRCI level with basis sets of up to aug‐cc‐pV5Z quality. Core electron correlation and relativistic contributions were also investigated. RCCSD(T)/aug‐cc‐pVQZ potential energy functions (PEFs) of the X̃ 1 A 1 and ã 3 B 1 states, and a CASSCF/MRCI/aug‐cc‐pVQZ PEF of the à 1 B 1 state of GeCl 2 are reported. Anharmonic vibrational wavefunctions of these electronic states of GeCl 2 , obtained variationally using the computed PEFs, are employed to calculate the Franck–Condon factors (FCFs) of the ã–X̃ and ÖX̃ transitions of GeCl 2 . Simulated absorption spectra of these transitions based on the computed FCFs are compared with the corresponding experimental laser‐induced fluorescence (LIF) spectra of Karolczak et al. [ J. Chem. Phys. 1993 , 98 , 60–70]. Excellent agreement is obtained between the simulated absorption spectrum and observed LIF spectrum of the ã–X̃ transition of GeCl 2 , which confirms the molecular carrier, the electronic states involved and the vibrational assignments of the LIF spectrum. However, comparison between the simulated absorption spectrum and experimental LIF spectrum of the ÖX̃ transition of GeCl 2 leads to a revision of vibrational assignments of the LIF spectrum and suggests that the X̃ 1 A 1 state of GeCl 2 was prepared in the experimental work, with a non‐Boltzmann vibrational population distribution. The X̃(0,0,1) level is populated over 4000 times more than expected from a Boltzmann distribution at 60 K, which is appropriate for the relative population of the other low‐lying vibrational levels, such as the X̃(1,0,0) and X̃(0,1,0) levels.