Warren S. Staker

Direct measurement of methylene removal rates by species containing the OH functional group

The technique of laser flash photolysis/laser absorption has been used to obtain absolute removal rate constants for singlet methylene (1CH2) with N2, ketene (CH2CO), H2O, D2O, methanol (CH3OH), ethanol (C2H5OH), and n-propanol (n-C3H7OH) at 296 ± 2 K. The rate constants were found to be (0.130 ± 0.012), (2.38 ± 0.18), (1.60 ± 0.17), (1.05 ± 0.13), (2.20 ± 0.19), (2.61 ± 0.23) and (4.15 ± 0.44)× 10–10 cm3 molecule–1 s–1, respectively. The removal rate constants for the alcohols are consistently greater than those for the corresponding alkanes.

The gas-phase reaction of SiH2 with dimethylether: kinetic evidence for direct formation of a donor–acceptor adduct

Abstract The kinetics of the title reaction have been investigated at 296 K (3–400 Torr in Ar and 3–50 Torr in SF 6 ), and between 298 and 434 K (5 Torr in Ar). The second-order rate constants increase by ca.×20 between 3 and 400 Torr (Ar) and ca.×6 between 3 and 50 Torr (SF 6 ). At 5 Torr Ar, an Arrhenius plot gives log (A/ cm 3 molecule −1 s −1 )=−13.71±0.13 and E a =−15.3±0.9 kJ mol −1 . The data are consistent with the formation of an H 2 Si…OMe 2 donor–acceptor adduct. RRKM/master equation modelling of the rate constants at 296 K gives a high pressure limiting value ( k ∞ ) of 6.6×10 −10 cm 3 molecule −1 s −1 and a binding energy of 96 kJ mol −1 for the adduct.

Direct measurement of singlet methylene removal rates by organic species containing the – O – and > C = O moieties

The technique of laser flash photolysis/laser absorption has been used to obtain absolute removal rate constants for singlet methylene 1CH2(a1A1) with dimethyl ether (CH3OCH3), acetaldehyde (CH3CHO), acetone (CH3COCH3), acetic acid (CH3CO2H), methyl formate (HCO2CH3), acetic anhydride (CH3CO2COCH3), and dimethyl carbonate (CH3OCO2CH3). The removal rate constants were found to be (1.80 ± 0.22), (2.81 ± 0.35), (4.48 ± 0.35), (5.71 ± 0.40), (2.82 ± 0.32), (5.27 ± 0.71) and (2.68 ± 0.28)× 10–10 cm3 molecule–1 s–1, respectively. Removal rate constants for the molecules containing the > CO moiety are considerably greater than those for the corresponding alkanes, but the removal rate constant for dimethyl ether is significantly less than that for the alkane analogue, propane. Removal rate constants were also remeasured for ethane (C2H6), ethene (C2H4) and methanol (CH3OH) and found to be (1.95 ± 0.48), (2.46 ± 0.23) and (3.69 ± 0.37)× 10–10 cm3 molecule–1 s–1, respectively.

Singlet methylene removal by saturated and unsaturated hydrocarbons

The technique of laser flash photolysis/laser absorption has been used to obtain absolute removal rate constants for singlet methylene, {sup 1}CH{sub 2} ({tilde a}{sup 1}A{sub 1}), with various saturated and unsaturated hydrocarbons. The removal rate constants for CH{sub 4}, C{sub 2}H{sub 6}, C{sub 3}H{sub 8}, C{sub 2}H{sub 4}, C{sub 3}H{sub 6}, C{sub 2}H{sub 2}, CH{sub 2}CCH{sub 2}, and C{sub 6}H{sub 6} were found to be in excellent agreement with previously reported results. Removal rate constrains were also measured for n-C{sub 4}H{sub 10}, i-C{sub 4}H{sub 10}, n-C{sub 5}H{sub 12}, c-C{sub 3}H{sub 6}, c-C{sub 6}H{sub 12}, 1-C{sub 4}H{sub 8}, cis-2-C{sub 4}H{sub 8}, trans-2-C{sub 4}H{sub 8}, and 1-C{sub 4}H{sub 6}, and determined to be (3.27 {+-} 0.15), (2.53 {+-} 0.11), (3.35 {+-} 0.24), (1.63 {+-} 0.08), (3.77 {+-} 0.21), (3.80 {+-} 0.20), (3.67 {+-} 0.16), (3.43 {+-} 0.16) and (4.05 {+-} 0.18) {times} 10 {sup {minus}10} cm{sup 3}/molecule {center_dot} s, respectively. This series of hydrocarbons forms the basis of a larger series of compounds containing a wide variety of organic functional groups. The removal rate constants are reported here, both as a series within its own right, and as a reference point for future work.

Singlet methylene removal by halogen-containing organic species

Abstract The technique of laser flash photolysis/laser absorption has been used to obtain absolute removal rate constants for singlet methylne, 1 CH 2 (a 1 A 1 ), with various halogen-containing organic species. The removal rate constants for CH 3 Cl, CH 2 Cl 2 , CHCl 3 , CCl 4 , CH 3 CCl 3 , CH 2 CHCl, CH 3 Br, CH 2 CHBr, ch 3 F, CF 4 , CHF 2 CFH 2 , C 2 F 6 CH 2 CHF, C 2 F 4 , C 6 H 5 F, p -C 6 F 2 and CF 3 COOCOCF 3 were measured and found to be (2.72±0.13), (3.36±0.19), (3.48±0.17), (3.35±0.21), (3.61±0.37), (3.21±0.16), (3.03±0.16), (3.54±0.19), (0.549±0.025), (0.169±0.018), (0.639±0.059), (0.212±0.031), (1.73±0.09), (0.509±0.062), (3.36±0.19), (2.59±0.26) and (2.00±0.14) × 10 −10 cm 3 molecule −1 s −1 , respectively. Comparisons are drawn between the reactivities of the various halide groups and with their hydrocarbon analogues.

Triplet Lifetimes, Solvent, and Intramolecular Capture of Isoxazolones

The first step in the photochemical decarboxylation of isoxazolones is the formation of the triplet state of the isoxazolone. We present evidence for the first time from flash laser photolysis of the lifetime of such species, and examples of their capture by solvent and by intramolecular cycloaddition.