Absolute rate coefficients of the reactions of CF2(a 3B1) with C3H8, C3H6, iso-C4H8 andC3H4 between 295 and 550 K

The rate coefficients of the removal of metastable electronically excited CF2((a) over tilde B-3(1)) by several hydrocarbons have been determined for the first time over an extended temperature range (295 K-550 K). CF2(B-3(1)) radicals were generated by pulsed laser photolysis Of C2F4 at 193 nm and real-time pseudo-first-order decays of the relative CF2(B-3(1)) concentration were obtained by monitoring the CF2(B-3(1) --> (1)A(1)) emission at 570-700 nm. Over the experimental temperature range, the rate coefficients of CF2 ((a) over tilde B-3(1)) removal by (di-)alkenes exhibited a marked negative temperature dependence: k(C3)H(6)(T) = (7.8+/-2.3) x 10(-13) exp[+(500 +/- 100)K /T] cm(3) S-1 molecule(-1), k(iso-C4)H(8)(T) = (1.4+/-0.2) x 10-(12) exp[+(762+/-36)K/T] cm(3) s(-1) molecule(-1), k(C3H4)(T) = (2.1+/-0,5) x 10(-13) exp[+(790+/-83)K/T] cm(3) s(-1) molecule(-1). For the removal of CF2 ((a) over tilde B-3(1)) by C3H8, the rate coefficient exhibited a small positive temperature dependence: k(C3H8)(T) = (6.5+/-2.2) x 10(-13) exp[-(252+/-130)K/T] cm(3) s(-1) molecule.