RESUMEN
Infrared (IR) action spectroscopy is utilized to characterize a prototypical carbon-centered hydroperoxyalkyl radical (â¢QOOH) transiently formed in the oxidation of volatile organic compounds. The â¢QOOH radical formed in isobutane oxidation, 2-hydroperoxy-2-methylprop-1-yl, â¢CH2(CH3)2COOH, is generated in the laboratory by H-atom abstraction from tert-butyl hydroperoxide (TBHP). IR spectral features of jet-cooled and stabilized â¢QOOH radicals are observed from 2950 to 7050 cm-1 at energies that lie below and above the transition state barrier leading to OH radical and cyclic ether products. The observed â¢QOOH features include overtone OH and CH stretch transitions, combination bands involving OH or CH stretch and a lower frequency mode, and fundamental OH and CH stretch transitions. Most features arise from a single vibrational transition with band contours well simulated at a rotational temperature of 10 K. In each case, the OH products resulting from unimolecular decay of vibrationally activated â¢QOOH are detected by UV laser-induced fluorescence. Assignments of observed â¢QOOH IR transitions are guided by anharmonic frequencies computed using second order vibrational perturbation theory, a 2 + 1 model that focuses on the coupling of the OH stretch with two low-frequency torsions, as well as recently predicted statistical â¢QOOH unimolecular decay rates that include heavy-atom tunneling. Most of the observed vibrational transitions of â¢QOOH are readily distinguished from those of the TBHP precursor. The distinctive IR transitions of â¢QOOH, including the strong fundamental OH stretch, provide a general means for detection of â¢QOOH under controlled laboratory and real-world conditions.