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

Abstract

The technique of laser flash photolysis/laser absorption has been used to obtain absolute removal rate constants for singlet methylene ' CH, (& 'A,) with dimethyl ether (CH,OCH,), acetaldehyde (CH,CHO), acetone (CH,COCH,), acetic acid (CH,CO,H), methyl formate (HCO,CH,), acetic anhydride (CH,C02COCH3), and dimethyl carbonate (CH,OCO,CH,). The removal rate constants were found to be (1.80 Ifr 0.22), (2.81 f 0.35), (4.48 & 0.35), (5.71 2 0.40), (2.82 f 0.32), (5.27 f 0.71) and (2.68 & 0.28) x lo-'' cm3 molecule-' s -' , respectively. Removal rate constants for t h e molecules containing t h e > C=O moiety are considerably greater than those for t h e corresponding alkanes, but t h e removal rate constant for dimethyl e t h e r is significantly less than that for t h e alkane analogue, propane. Removal rate constants were also remeasured for ethane (C2H,), ethene (C,H,) and methanol (CH,OH) and found to be (1.95 & 0.48), (2.46 f 0.23) and (3.69 & 0.37) x lo-'' cm3 molecule-' s -' , respectively.The simplest carbene, methylene (CH,), possesses a distinctive chemistry, playing significant roles in such reaction systems as flames and planetary atmospheres, and as a reactive intermediate in organic chemistry. The fundamental importance of methylene has resulted in a significant literature devoted to this species. Since the first study' of singlet methylene (2 'A1, abbreviated 'CH,) reaction rates using a direct method, several groups have measured bimolecular removal rate constants for 'CH, with a range of hydrocarb m s and inorganic molecules using laser-based methods.'-'Although reactions of 'CH, with numerous hydrocarbons have now been investigated, there has yet to be a systematic study of removal rate constants for reactions with a series of compounds containing specific organic functional groups. We are currently undertaking such a study and recently reported removal rate constants for some species containing the O H functional group.' Here we report preliminary results for 'CH, removal by species containing the -0and > C E O moieties. In this study the technique of laser flash photolysis/ laser absorption is again used to examine the reactions of 'CH, with dimethyl ether, acetaldehyde, acetone, acetic acid, methyl formate, acetic anhydride and dimethyl carbonate. The absolute rate constants for the removal of 'CH, by these compounds have been determined at ambient temperature. In addition, removal rate constants have been measured for ethane, ethene and methanol. There are differences in the removal rate constants reported by various g r o ~p s ~, ~, ' ~, ' 3 * 1 s for the last two species.

Temperature Dependences of Singlet Methylene Removal Rates

“…[13][14][15][16] We give here a brief overview and provide details relevant to the temperature dependence experiments. The same stainless steel reaction cell is used for the high-temperature work as was used for the ambient temperature studies.…”

Rate constants for the gas-phase reactions of germylene with CH3OCH3, CH3OH, CD3OD and D2O at ambient temperature

“…This effect has also been seen in our previous kinetic studies of singlet CH 2 and SiH 2 . [16][17][18][21][22][23][24][25][26][27][28] We have shown previously that the rate constants are independent of photolysis wavelength, indicating that vibrational relaxation is not an issue in this system. 9 The rate constants reported here were obtained with total cell pressures in the range 10-200 Torr.…”

Singlet Methylene Removal Rate Constants from the (0,1,0) Vibrational Level: Enhancement via Complex-Mediated Vibrational Relaxation

“…The particular apparatus and techniques used in our studies of singlet methylene have been presented in detail in previous publications describing our (0,0,0) ambient and temperature dependent studies [19,20,[22][23][24][25][26][27]. We here give a brief overview, and provide details relevant to the (0,1,0) experiments.…”

“…The second-order decay is obtained from a plot of the pseudo-first-order decay rate constants versus reactant pressure. Typical experimental and fitted traces have been presented in previous publications from this group, as have plots of the pseudo-first-order decay rate constants versus reactant pressure [19,20,[22][23][24][25][26][27]. The experiments are performed at ambient temperature (295 ± 2 K).…”