Generation and detection of alkyl peroxy radicals in a supersonic jet expansion

摘要

Alkyl peroxy radicals are synthesized in a supersonic jet expansion by the initial production of alkyl radicals and subsequent reaction with molecular oxygen.Parent ions CH_3OO~+/CD_3OO~+ are observed employing vacuum ultraviolet (VUV) single photon ionization/time-of-flight mass spectroscopy (TOFMS).Employing infrared (IR)+VUV photofragmentation detected spectroscopy,rotationally resolved infrared spectra of jet-cooled CH_3OO and CD_3OO radicals are recorded for the A~2A' <-X ~2A" transition by scanning the IR laser frequency while monitoring the CH_3 and CD_3 ion signals generated by the VUV laser.The band origins of the A ~2A' <-X~2A" transition for CH_3OO and CD_3OO are identified at 7381 and 7371 cm~(-1),respectively.Rotational simulation for the CH_3OO and CD_3OO 0_0~0 transitions of A<- X yields a rotational temperature for these radicals of approx 30 K.With the aid of ab initio calculations,two and five vibrational modes for the A ~2A' excited electronic state are assigned for CH_3OO and CD_3OO radicals,respectively.Both experimental and theoretical results suggest that the ground electronic state of the ions of ethyl and propyl peroxy radicals are not stable although their ionization energies (IE) are less than 10.5 eV.The C_2H_5OO~+/C_3H_7OO~+ cations can readily decompose to C_2H_5~+/C_3H} and O_2.This is partially responsible for the inability of IR+VUV photofragmentation spectroscopy to detect the near IR A<- X electronic transition for these radicals.