• “Absolute rate coefficients of the reaction of O(3P) atoms with selected chloroethenes”

M. B. BLANCO , P. M. COMETTO, R.A.TACCONE, S.I.LANE AND M.A.TERUEL

Florianópolis, SC, Brazil

Conferencia; 8th Latin American Conference on Physical Organic Chemistry (CLAFQO); 2005

CLAFQO

Rate coefficients at 298 K for the gas-phase reactions :                                             O(3P)    +    cis-ClHC=CHCl     à      Products                                           O(3P)    +     Cl2C=CH2             à      Products                                           O(3P)    +     Cl2C=CCl2            à      Products                                           O(3P)    +     CFCl=CHCl          à      Products   were determined to be (2.0 ± 0.4 ) , (11.3 ± 1.5 ), (1.9 ± 0.5) and (2.2 ± 0.4) x 10-13 cm3 molecule-1s-1, respectively.             The experiments were carried out using a discharge flow apparatus coupled with a chemiluminescence detection system under pseudo-first-order conditions with [O(3P)]o <<               [chloroethene]o. The oxygen atoms were generated by an electrodeless microwave discharge on a diluted O2/He mixture and were introduced to the main flow through a side port at the upstream end of the flow tube. The chloroethene was introduced into the tube at different distances from the detection system by a sliding injector. Experiments were performed under laminar flow conditions with efficient radial mixing, using helium as carrier gas. More than 95 % of the total gas flow is determined by the carrier gas, which thus determines the physical properties of the system allowing to work at constant total pressure in the flow tube.             The O(3P) concentration was monitored measuring the visible chemiluminescence resulting from the reaction of O(3P) atoms  with NO to produce electronically excited NO2*. The chemiluminescence signal, which is proportional to the oxygen atom concentration, was detected with a photomultiplier tube, amplified and displayed on an oscilloscope.             The effects of the extent and the position of the chlorine atom substitution on the molecule is  analyzed in relation to the reactivity of the chloroethenes towards attack by the electrophilic O(3P) atoms and compared with other atoms and radicals such as OH and Cl(2P).