Revealing the Ultrafast Energy Transfer Pathways in Energetic Materials: Time-Dependent and Quantum State-Resolved.

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Intramolecular vibrational energy transfer (IVET) is crucial for condensed-phase reactions but challenging to study due to complexity and computational cost.
• The role of doorway modes in mediating energy transfer from lattice phonons to intramolecular vibrations remains controversial and difficult to experimentally identify.

Purpose of the Study:

• To elucidate ultrafast energy transfer pathways in the energetic material β-HMX.
• To resolve coupled vibrational mode groups and identify specific energy transfer pathways.
• To confirm the mandatory role of doorway modes in phonon-to-vibration energy upconversion.

Main Methods:

• Utilized a combination of vibrational projection, statistical analysis, and the local quantum vibrational embedding (LQVE) method.
• Leveraged LQVE's time-dependent and quantum state-resolved capabilities to reveal microscopic mechanisms.
• Provided theoretical two-dimensional infrared (2D-IR) spectroscopy evidence.

Main Results:

• Resolved coupled vibrational mode groups and identified probable energy transfer pathways.
• Confirmed that doorway modes are a mandatory pathway for energy transfer.
• Determined the energy transfer timescale to be approximately 1 picosecond (ps).
• Provided theoretical 2D-IR evidence that aligns with experimental findings.

Conclusions:

• The study clarifies the fundamental mechanisms of ultrafast energy transfer in energetic materials.
• The developed methodologies offer theoretical support for controlling explosive behavior and designing new explosives.
• The approach is extendable to other condensed-phase materials for evaluating vibrational mode coupling.