Simplified Cartesian Basis Model for Intrapolyad Emission Intensities in the Bent-to-Linear Electronic Transition of Acetylene
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
The acetylene emission spectrum from the trans-bent electronically excited à state to the linear ground electronic $$\tilde{X}$$ state has attracted considerable attention because it grants Franck–Condon access to local bending vibrational levels of the $$\tilde{X}$$ state with large-amplitude motion along the acetylene ⇌ vinylidene isomerization coordinate. For emission from the ground vibrational level of the à state, there is a simplifying set of Franck–Condon propensity rules that gives rise to only one zero-order bright state per conserved vibrational polyad of the $$\tilde{X}$$ state. Unfortunately, when the upper level involves excitation in the highly admixed ungerade bending modes, ν4' and ν6', the simplifying Franck–Condon propensity rule breaks down—as long as the usual polar basis (with v and l quantum numbers) is used to describe the degenerate bending vibrations of the $$\tilde{X}$$ state—and the intrapolyad intensities result from complicated interference patterns between many zero-order bright states. In this article, we show that, when the degenerate bending levels are instead treated in the Cartesian two-dimensional harmonic oscillator basis (with vx and vy quantum numbers), the propensity for only one zero-order bright state (in the Cartesian basis) is restored, and the intrapolyad intensities are simple to model, as long as corrections are made for anharmonic interactions. As a result of trans ⇌ cis isomerization in the à state, intrapolyad emission patterns from overtones of ν4' and ν6' evolve as quanta of trans bend (ν3') are added, so the emission intensities are not only relevant to the ground-state acetylene ⇌ vinylidene isomerization, they are also a direct reporter of isomerization in the electronically excited state.
- Research Organization:
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- FG02-87ER13671
- OSTI ID:
- 1638458
- Journal Information:
- Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory, Vol. 119, Issue 5; ISSN 1089-5639
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Fundamental mechanisms for molecular energy conversion and chemical reactions at surfaces
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journal | August 2019 |
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