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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.

The technique of laser flash photolysisflaser absorption has been used to obtain an absolute removal rate constant of (3.85 2 0.18) X cm3 molecule-' s-l for singlet methylene, lCHz (glA1), with germane (Ge&) at ambient temperature. The removal rate constant is compared with the values for methane (CH4) and silane (SiH4) which have been determined previously. 0 1995 John Wiley & Sons, Inc.The simplest carbene, methylene (CHz), possesses a distinctive chemistry, playing significant roles in such reaction systems as flames, combustion, and planetary atmospheres. Carbenes form an important class of reactive intermediates in organic chemistry. The fundamental importance of CH2 has resulted in a significant literature devoted to this species in recent years [l]. An increased interest in the gas-phase kinetic studies of CH2 has occurred, largely due to the case with which the metastable singlet state (5lA1, abbreviated lCH2) may be observed by techniques such as laserinduced fluorescence (LIF) and laser resonant absorption (LRA). Since the first study [2] of lCH2 reaction rates using a direct method, several groups have measured bimolecular removal rate constants for lCH2 with a wide range of organic and inorganic molecules using laser-based methods 13-171.While removal rate constants have been measured for lCH2 reacting with a range of organic compounds, there has yet to be any detailed studies of reactions with organometallics. In this study we have used the technique of laser flash photolysisfiaser absorption to determine the absolute rate constant for the removal of lCH2 by germane (GeH4) at ambient temperature (298 * 2 K), apparently for the first time. The removal rate constant is compared with those measured previously for lCH2 with methane (CH4) and silane (SiH4).

The thermal unimolecular decomposition of hex-1-ene-3-yne (HEY) has been investigated over the temperature range 949-1230 K using the technique of very low-pressure pyrolysis (VLPP). One reaction pathway is the expected c5-c6 bond fission to form the resonance-stabilized 3-ethenylpropargyl radical. There is a concurrent process producing molecular hydrogen which probably occurs via the intermediate formation of hexatrienes and cyclohexa-1,3-diene. RRKM calculations yield the extrapolated high-pressure rate parameters at 1100 K given by the expressions 10'60'03 exp(-300.4 % 12.6 k J rnol-l/RT) s-' for bond fission and 10'32c04 exp(-247.7 2 8.4 k J mol-'/RT) for the overall formation of hydrogen. The A factors were assigned from the results of previous studies of related alkynes, alkenes, and-alkadienes.