The vibrational predissociation of the higher vibrational levels of the à state of the C₃Ar van der Waals complex

Yen-Chu Hsu^1*, Sheng-Chang Hsiao¹

¹Physics, National Central University, Taoyaun, Taiwan

* Presenter:Yen-Chu Hsu, email:ychsu@pub.iams.sinica.edu.tw

The study of the vibrational predissociation (VP) of a tetra-atomic van der Waals complex can be useful for understanding the intramolecular vibrational redistribution of a polyatomic molecule. Our previous work¹ showed that the Renner effect of the C₃(Ã) molecule at the 0 4- 0 and 0 2+ 0 levels on the VP processes of the pertinent C₃Ar levels is negligible. In this work, twelve ro-vibrational levels of the Ã-state complex lie at 1558-1660 cm-1 above the zero-point level have been studied, where the complex levels are associated with a second Renner pair at the 0 8- 0 and 0 4+ 0 levels and the 0 0 2 level of the C₃ molecule, to evaluate the contribution of the Renner effect, energy gap,² and vibrational mode to the VP processes. These two Renner pairs have comparable interaction strength, but the energy separations within each pair are different.³ The rotationally resolved excitation spectra and emission spectra have been recorded to provide the spectroscopic information and the detailed VP products of the Ã-state complex. The obtained fragment state distributions versus the recoiled translational energies of the fragments can deviate from the predictions of the energy gap law² or momentum gap law⁴ depending upon the excited vibrational modes and geometry of the complex. The predissociation fragments can be grouped into three: v₂, 1 v₂ 0, and 0 v₂ 1. The fragment states of these three groups only couple within each group through the final state interaction between different v₂ levels (low-frequency levels). Comparing results from our previous work¹ obtained at the low-lying complex levels (340-860 cm-1), we concluded that the final state interaction becomes important in this vibrational energy region and that the effects of vibrational modes, anharmonicities, and energy gap determine the VP processes of the à state of the C₃Ar complex. Weak effects such as spectroscopic perturbation, rotational angular momentum, Renner effect, and final state interaction² might modify the IVR or VP processes. The Renner effect affects the fragment distribution of the upper/lower Renner component weakly, but the angular momentum effects such as the P-propensity and the K-dependence of the VP processes reflect its presence.

References
1. Y.-J. Wang and Y.-C. Hsu, J. Chem. Phys. 153, 124303(2020).
2. J. A. Beswick and J. Jortner, Adv. Chem. Phys. XLVII , 363(1981).
3. C.-W. Chen, A. J. Merer, J.-M. Chao, and Y.-C. Hsu, J. Mol. Spectrosc. 263, 50(2010).
4. G. E. Ewing, J. Chem. Phys. 71, 3143(1979).

Keywords: vibrational predissociation, intramolecular vibrational redistribution, van der Waals compex, vibration mode, Renner effect