Ir. Sims et al., RATE CONSTANTS FOR THE REACTIONS OF CN WITH HYDROCARBONS AT LOW AND ULTRA-LOW TEMPERATURES, Chemical physics letters, 211(4-5), 1993, pp. 461-468
The pulsed laser-photolysis (PLP), time-resolved laser-induced fluores
cence (LIF) technique has been used to study the reactions of the CN r
adical with CH4, C2H6, C2H4, C3H6 and C2H2 at low and ultra-low temper
atures. Using a cryogenically cooled cell, rate constants have been de
termined for all five reactions at temperatures down to 160 K. The PLP
-LIF method has also been implemented in a CRESU (cinetique de reactio
n en ecoulement supersonique uniforme) apparatus providing rate consta
nts for the reactions of CN with C2H6, C2H4 and C2H2 at temperatures d
own to 25 K. The rate constants for CN + C2H4 and CN + C2H2 increase m
onotonically as the temperature is lowered from room temperature to 44
K but the values at 25 K are lower than those at 44 K. Remarkably, th
e rate constant for CN + C2H6 increases below 75 K, reaching its large
st value at 25 K. It is tentatively suggested that this behaviour may
reflect the transient formation of an energised van der Waals complex
which facilitates the subsequent abstraction of an H atom.