Identification and Self-Reaction Kinetics of Criegee Intermediates syn-CH 3 CHOO and CH 2 OO via High-Resolution Infrared Spectra with a Quantum-Cascade Laser.

The Criegee intermediates, carbonyl oxides produced in ozonolysis of unsaturated hydrocarbons, play important roles in atmospheric chemistry. The two conformers of CH3 CHOO exhibit distinct reactivity toward several atmospheric species, but a distinct conformer-specific probe is challenging because ultraviolet and infrared absorption bands of syn- and anti-CH3 CHOO overlap at low-resolution. Employing a quantum-cascade laser and a Herriott cell, we recorded the O-O stretching bands of CH2 OO and syn-CH3 CHOO in region 880-932 cm-1 at resolution 0.0015 cm-1 . In addition to completely resolved vibration-rotational lines of CH2 OO extending over 50 cm-1 , some spectral lines associated with hot bands were identified. Spectral lines solely due to syn-CH3 CHOO were also identified. Probing these lines, we determined the rate coefficient for the self-reaction of syn-CH3 CHOO to be kself = (1.6 ± 0.6 0.5 ) × 10-10 cm3 molecule-1 s-1 , about twice that of CH2 OO.