In search of the X{sub 2}BO and X{sub 2}BS (X = H, F) free radicals: Ab initio studies of their spectroscopic signatures

Journal Article · Sun Dec 28 04:00:00 EST 2014 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4904290· OSTI ID:22415423

The F{sub 2}BO free radical is a known, although little studied, species but similar X{sub 2}BY (X = H, D, F; Y = O, S) molecules are largely unknown. High level ab initio methods have been used to predict the molecular structures, vibrational frequencies (in cm{sup −1}), and relative energies of the ground and first two excited electronic states of these free radicals, as an aid to their eventual spectroscopic identification. The chosen theoretical methods and basis sets were tested on F{sub 2}BO and found to give good agreement with the known experimental quantities. In particular, complete basis set extrapolations of coupled-cluster single and doubles with perturbative triple excitations/aug-cc-pVXZ (X = 3, 4, 5) energies gave excellent electronic term values, due to small changes in geometry between states and the lack of significant multireference character in the wavefunctions. The radicals are found to have planar C{sub 2v} geometries in the X{sup ~2}B{sub 2} ground state, the low-lying A{sup ~2}B{sub 1} first excited state, and the higher B{sup ~2}A{sub 1} state. Some of these radicals have very small ground state dipole moments hindering microwave measurements. Infrared studies in matrices or in the gas phase may be possible although the fundamentals of H{sub 2}BO and H{sub 2}BS are quite weak. The most promising method of identifying these species in the gas phase appears to be absorption or laser-induced fluorescence spectroscopy through the allowed B{sup ~}-X{sup ~} transitions which occur in the visible-near UV region of the electromagnetic spectrum. The ab initio results have been used to calculate the Franck-Condon profiles of the absorption and emission spectra, and the rotational structure of the B{sup ~}-X{sup ~}0{sub 0}{sup 0} bands has been simulated. The calculated single vibronic level emission spectra provide a unique, readily recognizable fingerprint of each particular radical, facilitating the experimental identification of new X{sub 2}BY species in the gas phase.

• OSTI ID: 22415423
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 24 Vol. 141; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION
DIPOLE MOMENTS
ELECTRONIC STRUCTURE
EMISSION SPECTRA
EXCITATION
EXCITED STATES
EXTRAPOLATION
FLUORESCENCE SPECTROSCOPY
GROUND STATES
LASER RADIATION
MICROWAVE RADIATION
MOLECULAR STRUCTURE
MOLECULES
RADICALS
WAVE FUNCTIONS