Temperature Dependences of Singlet Methylene Removal Rates

Abstract

The technique of laser flash photolysis/laser absorption has been used to obtain absolute removal rate constants for singlet methylene, 1 CH 2 (a ˜1A 1 ), in the temperature range 298-462 K. The temperature dependences of the removal rate constants for N 2 , CH 4 , C 2 H 4 , C 2 H 6 , H 2 O, H 2 CO, CH 2 CO, CH 3 F, C 2 F 6 , and CH 3 OH were measured and the Arrhenius parameters determined. For the reacting species, CH 4 , C 2 H 4 , C 2 H 6 , H 2 O, H 2 CO, CH 2 CO, CH 3 F, and CH 3 OH, the rate constants exhibit negative temperature dependences with activation energies covering the range -0.7 ( 0.7 kJ mol -1 for CH 3 F to -3.5 ( 1.0 kJ mol -1 for CH 3 OH. In contrast, positive temperature dependences are observed for the nonreacting species, N 2 and C 2 F 6 , with activation energies of 1.8 ( 0.9 and 1.6 ( 2.0 kJ mol -1 , respectively. Good agreement was obtained with previously reported measurements for the N 2 , CH 4 , CH 2 CO, C 2 H 4 , and C 2 H 6 temperature dependences. For the nonreacting species, comparison is made with theoretical predicted temperature dependences for collision-induced intersystem crossing from 1 CH 2 (a ˜1A 1 ) to 3 CH 2 (X ˜3B 1 ).

Product Branching Ratio of the HCCO + NO Reaction

“…For comparison, Table 3 shows literature values of kinetic data for removal of 1 CH 2 as well as the isoelectronic species NH( 1 ∆) with several collision partners. [31][32][33][34][35] As shown, Xe is a faster relaxer of NH( 1 ∆) than N 2 by more than 2 orders H + CH 2 CO f products (6) 3 CH 2 + CH 2 CO f products (7) of magnitude. This is presumably due to the well-known heavy atom effect in promoting spin-forbidden processes.…”

An experimental study of the soot formed in the pyrolysis of acetylene

“…Studies carried out in flames indicated that the presence of water has an important thermal effect, reducing the flame temperature because of the heat capacity of water [19]. Since as the temperature decreases, the formation of soot is limited, and the addition of water should result in a decrease of soot formation.…”

The effect of temperature on collision induced intersystem crossing in the reaction of 1CH2 with H2

“…However, there have been measurements of the temperature dependence of 1 CH 2 +Ar, He, and N 2 [4,10,11], for which the CIISC yield is unity. The rate coefficients all increase with temperature; for example, for 1 CH 2 + Ar k CIISC increases from 5 to 15 · 10 À12 cm 3 molecule À1 s À1 between 295 and 860 K [4].…”