Cavity ringdown spectroscopy of the hydroxy-methyl-peroxy radical

Area of Science:

• Atmospheric Chemistry
• Chemical Physics
• Spectroscopy

Background:

• The hydroxy-methyl-peroxy radical (HMP) is a key intermediate in atmospheric oxidation processes.
• Understanding HMP's properties is vital for accurate atmospheric modeling.

Purpose of the Study:

• To experimentally determine the vibrational (OH stretch) and electronic (Ã ← X̃) spectra of HMP.
• To theoretically validate spectral assignments using density functional calculations.

Main Methods:

• Infrared Cavity Ringdown Spectroscopy (IR-CRDS) was used to detect spectra.
• Pulsed Laser Photolysis (PLP) initiated radical reactions in a flow reactor.
• Density Functional Theory (DFT) and Vibrational Perturbation Theory (VPT2) were employed for calculations.

Main Results:

• The ν1 vibrational spectrum origin was observed at 3622 cm⁻¹, consistent with theoretical predictions for the HMP-A conformer.
• The à ← X̃ electronic spectrum origin was observed at 7389 cm⁻¹, with vibronic bands assigned to torsional modes.
• Calculated potential energy surfaces and Franck-Condon factors reproduced experimental spectral intensities.

Conclusions:

• The study successfully characterized the vibrational and electronic spectra of HMP.
• Experimental data and theoretical calculations confirm the assignment of the observed spectra to the HMP-A conformer.
• The lowest energy conformer of the à state (HMP-B) was predicted but remains unobserved.