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Electronic spectra of YOH and YOD in the visible region: Strong vibronic coupling between the (B)over-tilde(1)II and (C)over-tilde(1)Sigma(+) states

TitleElectronic spectra of YOH and YOD in the visible region: Strong vibronic coupling between the (B)over-tilde(1)II and (C)over-tilde(1)Sigma(+) states
Publication TypeJournal Article
Year of Publication1999
AuthorsAdam, AG, Athanassenas, K, Gillett, DA, Kingston, CT, Merer, AJ, Peers, JRD, Rixon, SJ
JournalJournal of Molecular Spectroscopy
Date PublishedJul
Type of ArticleArticle
ISBN Number0022-2852

Laser excitation spectra of yttrium monohydroxide, YOH, have been recorded in the 500-625 nm wavelength region. Rotational analysis of bands of YOH and YOD has shown that the ground state is (X) over tilde(1)Sigma(+), with the structure r(0)(Y-O) = 1.948(6) Angstrom, r(0)(O-H) = 0.920(6) Angstrom; the bending frequency (nu(2), pi) is 313.73 cm(-1) (237.43 cm(-1) in YOD) and the Y-O stretching frequency (nu(3), sigma(+)) is 673.83 cm(-1) (655.34 cm(-1)). Two excited electronic states have been identified; they are assigned as (B) over tilde(1)Pi (16 449 cm(-1)) and (C) over bar(1)Sigma(+) (18 509 cm(-1)). Unusually strong vibronic coupling through the bending vibration occurs between these two states, which causes their vibrational structures to be highly irregular; assignments have only been possible following extensive wavelength-resolved fluorescence experiments. The vibronic coupling raises the bending frequency of the (C) over tilde(1)Sigma(+) state to 457 cm(-1) and reduces that of the lower Born-Oppenheimer component of the (B) over tilde(1)Pi state (which has A’ symmetry in the C, point group) to the extent that the molecule becomes nonlinear, with a potential barrier at the linear configuration of about 120 cm(-1). The presence of the potential barrier is clearly demonstrated by the level structure of YOD, where the Sigma(+) vibronic component of the 010 vibrational level (linear molecule notation) lies 1.4 cm(-1) below the 000 level. The upper Born-Oppenheimer component, which has A " symmetry, is unaffected; its bending frequency is similar to that of the ground state. Perturbations occur in both the (B) over tilde(1)Pi and (C) over tilde(1)Sigma(+) states; some of these represent local interactions between the two of them, but others are caused by higher vibrational levels of lower-lying "dark" electronic states. Over 40 ground state vibrational levels have been identified for both YOH and YOD from the wavelength-resolved fluorescence spectra. (C) 1999 Academic Press.

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