Comparison of singlet methylene removal rates by group IV hydrides

Abstract

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).

Ambient temperature removal rate constants for singlet methylene with some nitrogen and sulphur compounds

“…Reactant pressures were varied from 0.05 to 0.5 torr, with the upper limit imposed by fast removal rates. The quality of the plots of kist versus reactant pressure is similar to the many typical plots shown previously [15, [18][19][20][21][22]. The absolute removal rate constants, k l , obtained in this work are summarized in Tables 1 and 2.…”

A gas-phase kinetic study of the reaction of silylene with germane: absolute rate constants, temperature dependence and mechanism

“…k 3 E 3 For an added complication is the contribution of col-1CH 2 lisionally induced intersystem crossing (1CH 2 ] M ] 3CH 2 ] M) to the total removal rates, although the evidence 1CH 2 is that its contribution is small compared to reaction at room temperature. 15 The case of reaction with is interesting. The rate con-CH 4 stant for obtained by Chu, Beach and Jasinski22 1SiH 2 (2.5 ^0.5 ] 10~14 cm3 molecule~1 s~1) is regarded by the authors as an upper limit since, as they point out, as little as 0.01% of impurity reacting on every collision could account for this rate constant.…”

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).…”