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On the location of conical intersections in CH2BrCl using MS-CASPT2 methods
Tamas Rozgonyi1, Leticia Gonzalez
1Institute of Structural Chemistry, Chemical Research Center, Hungarian Academy of Sciences, 1025 Budapest, Pusztaszeri út 59-67, Hungary.
The Journal of Physical Chemistry. A
|August 25, 2006
Summary
This study investigates the photochemistry of CH2BrCl using multiconfigurational second-order perturbation theory. It identifies a conical intersection between electronic states, crucial for understanding the molecule's photochemical behavior.
Area of Science:
- Computational Chemistry
- Photochemistry
- Quantum Mechanics
Background:
- Understanding the photochemical reactions of halogenated methanes is crucial.
- Nonadiabatic crossings between electronic states play a significant role in molecular photochemistry.
- CH2BrCl presents an interesting case due to its low-lying singlet electronic states.
Purpose of the Study:
- To calculate two-dimensional potential energy surfaces for CH2BrCl's singlet states.
- To identify and characterize the conical intersection governing its photochemistry.
- To compare theoretical methods for conical intersection determination.
Main Methods:
- Multiconfigurational second-order perturbation theory (CASPT2).
- Calculation of potential energy surfaces for singlet states of CH2BrCl.
- Analysis of nonadiabatic crossings and conical intersections.
- Investigation of geometrical phase effects.
Main Results:
- Identified a near-degeneracy line between b1A' and c1A' states.
- Located a conical intersection on this near-degeneracy line.
- Compared conical intersection positions using CASSCF, SS-CASPT2, and MS-CASPT2.
- Validated the conical intersection using geometrical phase effects.
Conclusions:
- The photochemistry of CH2BrCl is controlled by a conical intersection between the A and B electronic states.
- MS-CASPT2 is effective in characterizing conical intersections and their associated phenomena.
- The study provides insights into the complex interplay of electronic states in photochemical reactions.
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