KINETIC-STUDY OF REACTIONS OF C2H5O AND C2H5O2 WITH NO AT 298K AND 0.55-2 TORR

The kinetics of C2H5O and C2H5O2 radicals with NO have been studied at 298 K using the discharge flow technique coupled to laser induced flu orescence (LIP) and mass spectrometry analysis. The temporal profiles of C2H5O were monitored by LIF. The rate constant for C2H5O + NO --> P roducts (2), measured in the presence of helium, has been found to be pressure dependent: k(2) = (1.25 +/- 0.04) x 10(-11), (1.66 +/- 0.06) x 10(-11), (1.81 +/- 0.06) x 10(-11) at P (He) = 0.55, 1 and 2 torr, r espectively (units are cm(3) molecule(-1) s(-1)). The Lindemann-Hinshe lwood analysis of these rate constant data and previous high pressure measurements indicates competition between association and disproporti onation channels: C2H5O + NO + M --> C2H5ONO; M (2a), C2K5O + NO --> C H3CHO + HNO (ab). The following calculated average values were obtaine d for the low and high pressure limits of k(2a) and for k(2b): k(2a)(0 ) = (2.6 +/- 1.0) X 10(-28) cm(6) molecule(-2) s(-1), k(2a)(proportion al to) = (3.1 +/- 0.8) x 10(-11) cm(3) molecule(-1) s(-1) and k(2b) ca . 8 x 10(-12) cm(3) molecule(-1) s(-1). The present value of k(2a)(0), obtained with He as the third body, is significantly lower than the v alue (2.0 +/- 1.0) x 10(-27), cm(6) molecule(-2) s(-1) recommended in air. The rate constant for the reaction C2H5O2 + NO --> C2H5O + NO2 (3 ) has been measured at 1 torr of He from the simulation of experimenta l C2H5O profiles. The value obtained for k(3) = (8.2 +/- 1.6) x 10(-12 ) cm(3) molecule(-1) s(-1) is in good agreement with previous studies using complementary methods. (C) 1995 John Wiley & Sons, Inc.