Kinetics and mechanism associated with the reactions of hydroxyl radicals and of chlorine atoms with 1-propanol under near-tropospheric conditions between 273 and 343 K

Rate constants for the reactions of OH radicals and Cl atoms with 1-propanol (1-C 3 H 7 OH) have been determined over the temperature range 273-343 K by the use of a relative rate technique. The value of k(Cl + 1-C 3 H 7 OH) = (1.69 ′ 0.19) × 10 - 1 2 cm 3 molecule - 1 s - 1 at 298 K and shows a small increase of 10% between 273 and 342 K. The value of k(OH + 1-C 3 H 7 OH) increases by 14% between 273 and 343 K with a value of (5.50 ′ 0.55) × 10 - 1 2 cm 3 molecule - 1 s - 1 at 298 K, and further when combined with a single independent experimentally determined value at 753 K gives k(OH + 1-C 3 H 7 OH) = 4.69 x 10 - 1 7 T 1 . 8 exp(422/T) cm 3 molecule - 1 s - 1 . which fits each data point to better than 2%. Two well-established structure-activity relationships for H abstraction by OH radicals give accurate predictions of the rate constant for OH + 1-C 3 H 7 OH, provided the β-CH 2 group is given an increased reactivity of a factor of about 2 over that for the structurally equivalent CH 2 group in alkanes at 298 K. A quantitative product analysis was carried out at 298 K for the Cl-initiated photooxidation of 1-C 3 H 7 OH, using both FTIR and gas chromatography. HCHO, CH 3 CHO, and C 2 H 5 CHO were the only major organic primary products observed, although HCOOH was found in much smaller amounts as a secondary product. A key characteristic of the analysis was that the initial values of the product ratio [CH 3 CHO]/[C 2 H 5 CHO] were effectively constant for NO pressures between 0.15 and 0.3 Torr, but fell by about 35% as the pressure fell to 0.0375 Torr. From a detailed consideration of the mechanism for the oxidation, it is suggested that C 2 H 5 CHO, CH 3 CHO (+HCHO), and 3 molecules of HCHO are formed uniquely from CH 3 CH 2 CHOH, CH 3 CHCH 2 OH and CH 2 CH 2 CH 2 OH radicals, respectively. On this basis, use of the product yields gives the branching ratios of 56, 30, and 14% for Cl atom reaction at the α-, β-, and γ-C-H positions in 1-C 3 H 7 OH at 298 K. Given the very low temperature coefficients involved, little change will occur over tropospheric temperature ranges.