QUENCHING OF CH2(B-1(1)(0,14,0)

Room temperature rate constants for removal of CH2(B-1(1)) in the (0,1 4,0) vibrational state by nine collision partners have been determined . These measurements and previously reported data corcerning the B-1(1 ) and 1A1 states have been analyzed within the framework of several ki netic models. Rate constants are larger than gas kinetic, with the exc eption of rare gases, SF6, CH4, and homonuclear diatomic molecules, su ggesting the important role played by long-range attractive forces in the collisional quenching. The application of Parmenter's model groups the quenchers around three main mechanisms of deactivation. The first set corresponds to rare gases and the second to the inorganic molecul es and aliphatic organic molecules, and the third one groups CO2 and n onaliphatic organic molecules. The application of the collision-comple x model to the first and the second group shows a good correlation, su ggesting that for rare gases the physical quenching is governed by dis persion forces whereas for inorganic and aliphatic organic molecules t he removal process is governed by attractive multipole forces and prob ably involves chemical reaction. This model fails for CO2 and nonaliph atic organic quenchers, where deactivation of the excited methylene by charge-transfer interactions seems to be dominant. The application of the Parmenter's model to quenching rate constants for the lowest sing let state of methylene, 1A1, indicates that only two removal mechanism s take place. The collision-complex model reveals that rare gases and N2 quench this state by a mechanism controlled by dispersion forces bu t with a probability about 1 order of magnitude lower than that obtain ed for the B-1(1) state. For quenchers whose reactive channels are ava ilable, this model indicates that their removal cross sections are com patible with a mechanism in which once collisional complex model is fo rmed the removal process proceeds with a moderately high probability i rrespective of the chemical nature of the quencher. The compact electr onic configuration of the 1A1 state does not allow the activation of t he charge-transfer interactions favoured for the particular open struc ture of methylene B-1(1).