Is C₃Ar a good system to study the intramolecular vibrational energy transfer?

Yen-Chu Hsu^1,2*, Yi-Jen Wang², Shan-Chang Hsiao¹

¹Physics, National Central University, Jongli, Tauyuan, Taiwan
²Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan

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

The energy transfer study is an important subject in the area of photo-physics and photo-chemistry. It provides us a mean to predict how soon the stored energy will be decayed and where it goes. Since The C₃Ar van der Waals (vdW) complex is studied in a molecular beam, this work will be focused on the intramolecular processes.
Despite that the C₂Ar vdW complex is a small molecular system, its first electronic state, ¹Π_u, has a strong vibronic coupling¹ and thus it has more vibrational levels than that of a Σ-state. Its second interesting feature is that the angular momentum P is a good quantum number, which is the sum of the electronic orbital angular momentum and bending vibrational angular momentum. Other features such as the spectroscopic information of C₃ is sufficiently known², the bending vibration of the ground electronic state is of large amplitude,³ and it is possible to carry out ab initio quantum calculation.⁴ All these features suggested that the A ̃ state of C₃Ar is a good system for the intramolecular vibrational energy transfer (IVET) study.
Our recent work² showed that the excited C₃Ar(A) levels below 800 cm^-1 undergo fast vibrational predissociation from their emission spectra. Other relaxation processes were founded to be quite limited. The Δv and ΔP-propensities of the VP processes were derived from the experimentally determined fragment-state branching ratios. Deviations from the known energy and momentum gap laws were also identified. In this work, emission spectra obtained from higher vibration levels will be included in the presentation. Our ultimate goal is to improve the understanding about the IVET processes and to modify the existing models, if possible.

Reference:
1.L. Gausset, G. Herzberg, A. Lagerqvist, and B. Rosen, Astrophys. J. 142, 45(1965).
2. Y.-J. Wang and Y.-C. Hsu, J. Chem. Phys. 153, 124303(2020).
3. M. Mladenovi´c, S. Schmatz, and P. Botschwina, J. Chem. Phys. 101, 5891 (1994).
4. A. J. Merer, Y.-C. Hsu, Y.-R. Chen, and Y.-J. Wang, J. Chem. Phys. 143, 194304
(2015).

Keywords: van der Waals complex, C₃Ar, vibrational energy transfer, vibrational predissociation