REAL-TIME KINETICS OF THE UPTAKE OF CLONO2 ON ICE AND IN THE PRESENCEOF HCL IN THE TEMPERATURE-RANGE LESS-THAN-OR-EQUAL-TO-T-LESS-THAN-OR-EQUAL-TO-200K
R. Oppliger et al., REAL-TIME KINETICS OF THE UPTAKE OF CLONO2 ON ICE AND IN THE PRESENCEOF HCL IN THE TEMPERATURE-RANGE LESS-THAN-OR-EQUAL-TO-T-LESS-THAN-OR-EQUAL-TO-200K, The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 101(10), 1997, pp. 1903-1911
Pulsed dosing and steady state experiments of CIONO2 on ice at 180 and
200 K studied in a low pressure flow reactor reveal a temperature-ind
ependent reactive uptake coefficient gamma of 0.2 +/- 0.05 at Limiting
doses and low flow rates of 10(14) molecules per pulse and 10(14) mol
ecules s(-1), respectively. The reaction involves the formation of a p
recursor in a slow process releasing HOCl. This precursor does not int
eract with HCl. The reaction of CIONO2 with HCl was studied under puls
ed, concurrent, and sequential flow conditions and was found to follow
a direct mechanism. The formation of Cl-2 occurs promptly on the time
scale of several tens of milliseconds. The reactive uptake coefficien
t at equivalent flow rates of CIONO2 and HCl was measured to be 0.14 /- 0.05 and 0.26 +/- 0.05 at 200 and 180 K, respectively. At a 3-fold
excess of HCL gamma increases to 0.24 +/- 0.05 and 0.34 +/- 0.05 at 20
0 and 180 K, respectively. HOCl is found to interact with ice at T > 1
73 K and pressures of approximately 10(-6) Torr only up to the extent
of 5% of a monolayer beyond which it saturates. Arguments are put forw
ard in favor of an ionic displacement mechanism in both reactions. The
difference between the precursor mechanism of CIONO2 interaction on i
ce and the direct interaction of CIONO2 with HCl on ice may have ramif
ications for atmospheric chemistry which are briefly discussed.