Fig 4 . Energetic of the reaction between CI and HCl in water
cluster.
The first reaction route is normal proton abstraction by CI from HCl
which proceed via TS1 with a barrier of 13.56 kcal/mol and
generates a chloride radical, which can further initiate chain
reactions. The second reaction channel involves 1,3-insertion of HCl to
CI which forms a 5-memebered TS2 with a barrier of 17.75
kcal/mol. This TS2 gives a relevant INTClCH2OOH (chlorinated methylhydroxyperoxide) or
thermally fragmented into chlorinated methoxy and hydroxyl radicals
(P2 ). INT may lead to the most stable products
chlorinated methanal and water (P3 ) via a cyclic TS3 .
The energy barrier for this process is 19.1 kcal/mol. The formation ofP3 is highly exergonic and is the most stable product.
The rate constant of each reaction channel as well as the overall rate
constant of the reaction at 298 K are calculated using equation (1). It
should be noted that rate constants are calculated only for the
exergonic pathway. The calculated rate constants at 298 K and 1atm are
k1 = 2.10 X 10-12cm3 molecules-1s-1 and k3 = 2.41 X
10-11 cm3molecules-1 s-1 and the overall rate
constant kTotal (= k1 +
k3) is 2.63 X 10-11cm3 molecules-1s-1. The rate constant k2 is not
calculated as the reaction channel is endergonic. The calculated overall
rate constant for the reaction between the CI and hydrochloric acid is
in good agreement with the experimental rate constant 4.0 X
10-11 cm3molecule‑1 s-1.17
We have also calculated the percentage of the branching ratios (B.R) of
each reaction channels by using the relation %B.R =
(ki/kTotal) X 100. The calculate value
of B.R for the reaction channel R1 and R3 are 8% and 92% which
indicates that the formation of P3 via the cyclic TS3is the most dominant.
3.4 Reaction between formic acid and CI: Four reaction pathways
have been shown for the reaction between CI and formic in this study as
shown in Fig 5.