Infrared Spectrum of the Propargyl Peroxyl Radical, HC≡C—CH2OO X̃ 2A′′†

When the propargyl radical, HCCCH2, and O2 are codeposited onto a cold argon matrix, a chemical reaction ensues; infrared absorption spectra reveal the formation of the propargyl peroxyl radical: HC═...C—...CH2XB21+O2 → trans-HC═C—CH2OOXA2 We do not observe the isomeric adduct, CH2═C═CHOO X 2A′′. The propargyl radicals are produced by a hyperthermal nozzle while a second nozzle alternately fires bursts of O2/Ar at the 20 K matrix. The absorption spectra of the radicals are measured using a Fourier transform infrared spectrometer. We observe 13 of the 18 fundamental infrared bands of the propargyl peroxyl radical in an Ar matrix at 20 K. The experimental frequencies (cm−1) of trans-HC≡C−CH2OO X 2A′′ are assigned. The a′ modes are ν1 = 3326, ν2 = 2960, ν3 = 2148, ν4 = 1440, ν5 = 1338, ν6 = 1127, ν7 = 982, ν8 = 928, ν9 = 684, and ν10 = 499 cm−1, while the a′′ modes are ν14 = 1218, ν15 = 972, and ν16 = 637 cm−1. Linear dichroism spectra were measured with photo-oriented HCCCH2OO radical samples to establi...