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Published on: September 25, 2017
Ultrafast S1 to S0 internal conversion dynamics for dimethylnitramine through a conical intersection.
Yuanqing Guo1, Atanu Bhattacharya, Elliot R Bernstein
1Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872, USA.
The Journal of Physical Chemistry. A
|March 1, 2011
Summary
Ultrafast internal conversion (IC) in dimethylnitramine (DMNA) occurs in ~50 fs via a conical intersection. This rapid process, crucial for energetic materials, channels energy into vibrations, initiating decomposition pathways.
Area of Science:
- Physical Chemistry
- Chemical Dynamics
- Spectroscopy
Background:
- Nonadiabatic processes, like internal conversion (IC), are key to energetic material decomposition.
- Excitation energy can be stored as vibrational energy in the ground state, leading to bond dissociation.
Purpose of the Study:
- To determine the ultrafast internal conversion (IC) dynamics of dimethylnitramine (DMNA).
- To elucidate the role of conical intersections (CIs) in DMNA's excited-state decay.
Main Methods:
- Femtosecond (fs) pump-probe spectroscopy using 271 nm pump and 405.6 nm probe pulses.
- Complete active space self-consistent field (CASSCF) calculations to model potential energy surfaces and CIs.
Main Results:
- DMNA exhibits a very short S(1) excited state lifetime of approximately 50 ± 16 fs.
- Ultrafast IC from S(1) to S(0) is facilitated by an (S(1)/S(0)) conical intersection (CI).
- The decay pathway involves an out-of-plane bending mode of the NO(2) group.
Conclusions:
- The study identifies a conical intersection as the primary mechanism for rapid excited-state decay in DMNA.
- The observed IC dynamics are critical for understanding the initial decomposition steps of nitramine energetic materials.
- 271 nm excitation does not lead to adiabatic NO(2) elimination on the S(1) potential energy surface.
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