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Electronic State Spectroscopy of Nitromethane and Nitroethane.

Luiz V S Dalagnol1, Márcio H F Bettega1, Nykola C Jones2

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This study investigates photoabsorption cross-sections for nitromethane and nitroethane, revealing new absorption features. The findings help determine their atmospheric photolysis lifetimes and understand their photodissociation dynamics.

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Area of Science:

  • Physical Chemistry
  • Atmospheric Chemistry
  • Quantum Chemistry

Background:

  • Nitromethane and nitroethane are important industrial chemicals.
  • Understanding their atmospheric behavior is crucial for environmental impact assessments.

Purpose of the Study:

  • To measure high-resolution photoabsorption cross-sections for nitromethane and nitroethane.
  • To analyze new absorption features and assign them to specific electronic excitations.
  • To determine photolysis lifetimes and evaluate photodissociation dynamics in the terrestrial atmosphere.

Main Methods:

  • High-resolution photoabsorption spectroscopy in the 3.7-10.8 eV range.
  • Time-dependent density functional theory (TD-DFT) calculations for spectral interpretation.
  • Analysis of potential energy curves along the C-N reaction coordinate.

Main Results:

  • New absorption features attributed to vibronic excitations (valence, Rydberg, mixed) were observed for both molecules.
  • Nitroethane exhibits broader bands than nitromethane, attributed to side-chain effects.
  • Photolysis lifetimes were calculated, and pre-dissociative character was found to be higher in nitromethane.

Conclusions:

  • The study provides new insights into the electronic structure and atmospheric reactivity of nitromethane and nitroethane.
  • TD-DFT calculations aid in interpreting complex photoabsorption spectra.
  • Differences in photodissociation dynamics are linked to molecular structure and internal degrees of freedom.