Kinetics of the reactions of OH(X (2)Pi) radicals with 1,3-dioxolane and selected dialkoxy methanes

The gas-phase reaction of OH(X(2)Pi) radicals with 1,3-dioxolane was invest igated in the temperature range 250-550 K. The reactions of OH(X(2)Pi) with di-isopropoxy methane (DiPM), di-n-butoxy methane (DnBM) and di-sec-butoxy methane (DsBM) were studied below room temperature down to 250 K. The expe riments were carried out in argon, mostly at a total pressure of 400 Torr. A few additional measurements for the reaction OH + 1,3-dioxolane at 50 Tor r exhibited that this reaction is independent of total pressure in the rang e investigated. OH radicals were generated by excimer laser photolysis of H 2O2 and were detected by laser-induced fluorescence. For the OH + 1,3-dioxo lane reaction, no temperature dependence was observed within the experiment al errors. The bimolecular rate coefficient is well described by k(OH+dioxo lane) (T) = (8.2 +/- 1.3) x 10(-12) cm(3) s(-1). The rate coefficients meas ured for the reactions of OH with DiPM, DnBM and DsBM are discussed togethe r with literature data obtained for higher temperatures. The Arrhenius plot s for each reaction exhibited concave upward curvatures. From these data, t he following Arrhenius expressions were derived (with T in K and E-0 in kJ mol(-1)): k(OH + DiPM)(T) = (6.2 +/- 8.5) x 10(-14) x (T/298)(4.3 +/- 1.0) x exp[(15. 8+/-3.2)/RT] cm(3) s(-1), k(OH + DnBM)(T) = (3.9+/-2.8) x 10(-13) x (T/298)(2.6 +/- 0.5) x exp[(13.7 +/- 1.2)/RT] cm(3) s(-1), k(OH + DsBM)(T) = (1.4 +/- 0.7) x 10(-13) x (T/298)(3.6 +/- 0.4) x exp[(11. 5 +/- 0.9)/RT] cm(3) s(-1). The given expressions for the rate coefficients are only valid within the l imited temperature range of the present experiments. Since the equations ar e not theoretically supported, an extrapolation to other temperatures is no t allowed.