High Resolution Rovibrational Study of the Coriolis-coupled v12 and v15 Modes [1.1.1] Propellane
Alfons Weber, Robynne Kirkpatrick, Tony Masiello, N Jariyasopit, J Nibler, Jintao Zhang, Thomas A. Blake
Infrared spectra of the small strained cage molecule [1.1.1] propellane have been obtained at high resolution (0.0015 cm-1) and the J, K, and l rovibrational structure has been resolved for the first time. We recently used these spectra to obtain combination-differences to deduce ground state parameters for propellane; over 4,100 differences from five fundamental and four combination bands were used in the fitting process. The combination-difference approach eliminates potential errors caused by localized perturbations in the upper state and gave well-determined ground state parameters. In the current work, these ground state constants were fixed when fitting the upper state parameters for the ¿12(e¢) perpendicular and ¿15(a2") parallel bands. Over 4000 infrared transitions were fitted for each band, with J, K values ranging up to 71, 51 and 92, 90 respectively. While the transition wavenumbers for both bands can be fit nicely using separate analyses for each band, the strong intensity perturbations observed in the weaker ¿12 band indicated that Coriolis coupling between the two modes was significant and should be included. Due to correlations with other parameters, the Coriolis coupling parameter zy15,12a for the ¿15 and ¿12 interaction is poorly determined by a transition wavenumber fit alone but, fortunately, the intensity perturbations gave useful added constraints on zy15,12a. By combining the wavenumber fit with a fit of experimental intensities, a value of -0.42 was obtained, quite close to a value of -0.44 predicted by Gaussian ab initio density functional calculations using a cc-PVTZ basis. This intensity fit also yielded a dipole derivative ratio of 36.5, in reasonable agreement with a value of 29.2 predicted by the ab initio calculations. This ratio is unusually high due to large charge movement as the novel central Caxial-Caxial bond is displaced along the symmetry axis of the molecule for the ¿15 mode.
[1.1.1]propellane, Coriolis couplings, high-resolution infrared spectrum, intensity perturbations, Nu 12 and NU 15 modes
, Kirkpatrick, R.
, Masiello, T.
, Jariyasopit, N.
, Nibler, J.
, Zhang, J.
and Blake, T.
High Resolution Rovibrational Study of the Coriolis-coupled v12 and v15 Modes [1.1.1] Propellane, Journal of Molecular Spectroscopy, [online], https://doi.org/10.1016/J.JMS.2008.09.013
(Accessed June 4, 2023)