RATE CONSTANTS AND KINETIC ISOTOPE EFFECTS IN THE REACTIONS OF ATOMICCHLORINE WITH N-BUTANE AND SIMPLE ALKENES AT ROOM-TEMPERATURE

Rate constants for the reactions of chlorine atoms with n-butane and s imple alkenes, as well as most of their deuterated analogs, were studi ed at room temperature using two independent techniques. Using a fast flow discharge system (FFDS), the decay of chlorine atoms in 1 Ton He was followed using resonance fluorescence at 135 nm. In relative rate (RR) studies the decay of the organic was followed, relative to a refe rence compound, using GC-FID when they both reacted with chlorine atom s. These RR measurements were performed at 1 Ton in N-2 and at I atm i n both N-2 and air. The results of the FFDS and RR studies at I Ton we re generally in excellent agreement with each other and, where availab le, with literature data. Discrepancies appear to exist at 1 atm for i soprene, where the addition portion of the rate constant measured in t his laboratory is 40% higher than a value for k(infinity) reported rec ently by Bedjanian et al.(40) Our rate constant for 1,3-butadiene is 2 5% smaller than that of Bierbach et al.(39) Rate constants measured in these studies which have not been previously reported in the literatu re are as follows (in units of cm(3) molecule(-1) s(-1), with the erro rs being the statistical 2 sigma errors): C3D6 (4.1 +/- 0.8) X 10(-11) in I Torr He, (4.3 +/- 1.0) x 10(-11) in 1 Ton Nz, and (2.3 +/- 0.3) x 10(-10) in 1 atm N-2 or air; 1-C4H8 (1.0 rt 0.1) x 10(-10) in 1 Ton: He, (1.2 +/- 0.2) x 10(-10) in 1 Ton N-2, and (2.2 +/- 0.3) x 10(-10) at I arm Nz or air; 1-C4D8 (1.0 +/- 0.2) x 10(-10) in I Ton He, (1.2 +/- 0.2) x 10(-10) in I Ton Nz, and (2.0 +/- 0.4) x 10(-10) in 1 atn N -2 or air; n-C4D10 (1.6 +/- 0.1) x 10(-10) averaged over all pressures and carrier gases. Deuteration results in a normal kinetic isotope ef fect (KIE) for direct hydrogen abstraction, but an inverse kinetic iso tope effect for addition to the double bond. The KTE (k(H)/k(D)) for n -butane was measured to be 1.4 +/- 0.2. For ethene, an inverse KIE was measured, 0.74 +/- 0.06 at 1 atm in Nz or air compared to an average of 0.35 at 1 Ton in NZ or He reported in earlier studies.(29) The KIEs for the larger alkenes were unity within experimental error. For prop ene at 1 Ton, the inverse KIE for addition is largely counterbalanced by a normal KIE for abstraction of an allylic hydrogen. For the larger alkenes, this result is consistent with expectations because addition is close to the high-pressure limit even at 1 Ton and abstraction is expected to play a minor role in the overall reaction. The atmospheric implications of these measurements are discussed.