Spectroscopic and Kinetic Properties of HO₂ Radicals and the Enhancement of the HO₂ Self Reaction by CH₃OH and H₂O

Abstract

The line center absorption cross sections and the rate constants for self-reaction of hydroperoxy radicals (HO(2)) have been examined in the temperature range of 253-323 K using pulsed laser photolysis combined with tunable diode laser absorption in the near-IR region. The transition probed was in the 2nu(1) OH overtone transition at 1506.43 nm. The temperature dependence of the rate constant (k) for the HO(2) + HO(2) reaction was measured relative to the recommended value at 296 K, giving k = (3.95 +/- 0.45) x 10(-13) x exp[(439 +/- 39)/T] cm(3) molecule(-1) s(-1) at a total pressure of 30 Torr (N(2) + O(2)). After normalizing our determination and previous studies at low pressure, we recommend k = (2.45 +/- 0.50) x 10(-13) x exp[(565 +/- 130)/T] cm(3) molecule(-1) s(-1) (0 < P < 30 Torr, 95% confidence limits). The observed rate coefficient, k(obs), increases linearly with CH(3)OH concentration, and the enhancement coefficient (k'), defined by k(obs) = k + k'[CH(3)OH], is found to be (3.90 +/- 1.87) x 10(-35) x exp[(3849 +/- 135)/T] cm(6) molecule(-2) s(-1) at 30 Torr. The analogous water vapor enhancement coefficient (k'') is (1.16 +/- 0.58) x 10(-36) x exp[(4614 +/- 145)/T] cm(6) molecule(-2) s(-1). The pressure-broadened HO(2) absorption cross section is independent of temperature in the range studied. The line center absorption cross sections at 1506.43 nm, after correction for instrumental broadening, are (4.3 +/- 1.1) x 10(-19), (2.8 +/- 0.7) x 10(-19), and (2.0 +/- 0.5) x 10(-19) cm(2)/molecule at total pressures of 0, 30, and 60 Torr, respectively (95% confidence limits).

Detection of HO2in an atmospheric pressure plasma jet using optical feedback cavity-enhanced absorption spectroscopy

“…A wide class of cavity-enhanced spectroscopy techniques have been developed such as cavity ring-down spectroscopy (CRDS), off-axis cavityenhanced absorption spectroscopy (CEAS), optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) [17,18]. Of these variants, CRDS has been the method of choice for the detection of HO 2 utilizing absorption bands in the near-infrared (NIR) range [3,[19][20][21], although its detection using NICE-OHMS was also reported [22]. Similarly, CRDS has been employed for the detection of species in plasmas.…”

Computational study of hexanal peroxy radical–water complexes

“…It is speculated that the measured increase in the reaction rate coefficient is due to the formation of the HO 2 -H 2 O complex as one step in the reaction mechanism. A similar rate enhancement is also observed for the HO 2 self-reaction in the presence of CH 3 OH and NH 3 , but not CH 4 [4][5][6], suggesting that such enhancements are likely the result of OAHÁÁÁO or NAHÁÁÁO hydrogen-bond interactions between the radical and the interacting species.…”

Measurements of nitrogen-broadening coefficients in the ν3 band of the hydroperoxyl radical using a continuous wave quantum cascade laser

“…Spectroscopic properties of these absorption bands have been widely examined and the near-IR absorption bands were probed to study HO 2 kinetics [6][7][8][9][10][11][12][13][14][15][16]. Taatjes and Oh [7] detected HO 2 by the 2m 1 band at 1.5 lm using wavelength modulation spectroscopy.…”

“…Fittschen et al [11][12][13] measured the line strengths and air-broadening coefficients of HO 2 in the 2m 1 band using continuous wave cavity ring-down spectroscopy (cw-CRDS) coupled to laser photolysis. The line center absorption cross-sections of the 2m 1 absorption were determined to be in the order of 10 À19 cm 2 molecule À1 at tens of Torr [6,7,[11][12][13][14]. Kanno et al [16] measured the nitrogen-and water-pressure-broadening coefficients of the HO 2Ã 2 A 0 X2 A 00 band in the near-infrared region of 1.42 lm using TTFMS.…”