Infrared Spectrum of the Propargyl Peroxyl Radical, HC C-CH2OO (X)(2)A'

Evan B. Jochnowitz, Xu Zhang, Mark R. Nimlos, Bradley A. Flowers, John F. Stanton, G. Barney Ellison

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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-CH22B1 + O 2→trans-HC=C-CH2OOX̃2A We do not observe the isomeric adduct, CH2=C=CHOO X̃ 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 X̃ 2A″ are assigned. The a' modes are V1 = 3326, V2 = 2960, V3 = 2148, V4 = 1440, V5 = 1338, V6 = 1127, V7 = 982, V8 = 928, V9 = 684, and v10 = 499 cm-1, while the a′ modes are v 14 = 1218, V15 = 972, and V16= 637 cm -1. Linear dichroism spectra were measured with photo-oriented HCCCH2OO radical samples to establish the experimental polarizations of several vibrational bands. The experimental frequencies (v) for the propargyl peroxyl radical are compared to the anharmonic frequencies (v) resulting from electronic structure calculations. We have used CBS-QB3 electronic structure calculations to estimate the peroxyl bond energies: δH 298(trans-HC=CCH2-OO -CH2CCH X̃2B, + O2) = 19 ± 1 kcal mol-1 and δH298(transCH2=C=CH-OO -CH2CCH X̃ 2B1 + O2) = 21 ± 1 kcal mol -1. The experimental thermochemistry for C3H3́ reacting with oxygen has been reanalyzed as δrxnH 298(HCCCH2 + O2→ CH3=C==O + HCO) = -83 ± 3 kcal mol-1; δrxnH 298(HCCCH2 + O2→CH3CO + CO) = -111 ± 3 kcal mol-1; δrxnH 298(HCCCH2 + O2 -CH2CHO + CO) = -106 ± 4 kcal mol-1; δrxnH298(HCCCH2 + O2→HCHO + HCCO) = -67 ± 4 kcal mol-1; δrxnH298(HCCCH2 + O2→ CH2CH + CO2) = -105 ± 3 kcal mol-1.

Original languageAmerican English
Pages (from-to)1498-1507
Number of pages10
JournalJournal of Physical Chemistry A
Issue number3
StatePublished - 2010

NREL Publication Number

  • NREL/JA-510-47575


  • HCCCH2
  • propargyl peroxyl radical


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