Ultrafast dissociation dynamics of nitromethane: Enhanced efficiency under near-infrared vs ultraviolet excitation

Nitromethane is an essential energetic material with diverse technological applications. While numerous studies have independently investigated its dissociation dynamics under ultraviolet (UV) or near-infrared (NIR) excitation, comparative analyses between these spectral regimes at ultrafast temporal and microscopic spatial resolutions are limited. Here, employing real-time time-dependent density functional theory molecular dynamics simulations, we represent the first detailed microscopic comparison of nitromethane dissociation induced by NIR (1.55 eV) and UV (6.8 eV) laser excitations. Both excitation wavelengths initially drive C-N bond elongation during irradiation, followed by relaxation post-illumination. However, at sufficiently strong laser fields, immediate bond cleavage occurs within the irradiation period, underscoring the critical role of wavelength and intensity in reaction dynamics. Our simulations notably reveal significantly enhanced dissociation rates and efficiencies under NIR excitation compared to UV at equivalent intensities. This improved efficiency arises from distinct nonlinear multiphoton excitation pathways and pronounced thermal effects, promoting substantial molecular distortions and rapid energy transfer. These findings elucidate wavelength-dependent dissociation mechanisms, offering valuable insights to develop safer and more efficient laser-driven initiation strategies for nitroalkyl energetic materials.