Dissociation attachment

Martel R, Avouris Ph and Lyo l-W 1996 Molecularly adsorbed oxygen species on Si(111)-(7 7) STM-induced dissociative attachment studies Science 272 385... 

The initial kinetic energy of 0 ions produced by dissociative attachment in 02 at an electron energy of 6.9 e.v. may be determined from Equation 4 to be 1.64 e.v. using values of 1.465 e.v. (1) for A(0) and 5.09 e.v. (7) for D(O—O). The residence time for 0 ions calculated from Equation 1 is 6.0 X 10 7 sec. at 10 volts repeller potential. Rate constants for Reaction 6 determined from data at varying Vr are shown in Table I and are seen to increase sharply with increasing repeller potential, as expected for an endothermic process. 

Since under Green s conditions, a 10-7 cm.3 molecule-1 sec.-1 (unpublished experiments at AeroChem), n+ ne- 1011 cm.-3, /iH2o 3 X 1017 cm.-3, and n0h- 109 cm.-3, then kz 3 X 10-16 cm.3 molecule-1 sec.-1 This is some three orders of magnitude greater than the maximum value of kz calculated on the basis of Buchel nikova s data. Therefore, dissociative attachment of electrons to water is too slow to account for the observed concentrations of negative ions. 

Consideration of work by Buchel nikova (4) on the dissociative attachment of electrons to HC1 leads to the conclusion that k4 is given approximately by k4 10-10 e 20 mtRT cm.3 molecule-1 sec.-1 Since K 4 2 X 10-3 el8 miRT at 2000°K., 4 10 13 cm.3 molecule-1 sec.-1 This is considerably smaller than rate constants for other exothermal ion-molecule reactions, which probably reflects the importance of participation of molecular vibrational energy in such reactions. Remember, however, that the uncertainty in 4 is probably at least an order of magnitude. 

Dimensionless amplitude, 141 Directional bremsstrahlung, 131 Displacive excitation of coherent phonons (DECP), 27, 56 Dissociative attachment, 103 Double plasma mirror (DPM), 194 Dual energy subtraction imaging, 178... 

Collisions of some halogen bearing molecules, such as SF6, with Rydberg atoms result in attachment of the Rydberg electron to the molecule to form a negative molecular ion. Simple attachment, dissociative attachment, and attachment followed by autodetachment have all been observed. Collisions with attaching molecules are an excellent example of a process dominated by the electron... 

Among the processes leading to annihilation of free electrons, the most efficient is the dissociative recombination of an electron with a molecular ion. At small electron energies the cross section of such processes exceeds 10 13 cm2. 240 The cross sections for other types of recombination are much smaller. The cross section of dissociative attachment of an electron to a neutral molecule can vary within broad limits from 10 23 to 10 14 cm2, 223 243-244 and is the largest for halogen-containing molecules. 

At lower altitudes where significant concentrations of ozone exist, O- ions are generated by dissociative attachment [reaction (10b)]. These electron attachment processes and the laboratory techniques used to determine their rate coefficients were reviewed some time ago by Phelps1 S4 In the stratosphere and troposphere, negative ions can also be generated by dissociative attachment reactions of thermalised electrons with pollutants1 s5,1561 such as the freons e.g. 

Nesbet, R.K. (1996). Nonadiabatic phase-matrix method for vibrational excitation and dissociative attachment in electron-molecule scattering, Phys. Rev. A 54,... 

The complex-potential model originated as a qualitative explanation of dissociative attachment [18]. A fixed-nuclei electronic resonance is described by a complex potential whose width goes to zero at the crossing point with the molecular ground-state potential, and remains zero if the resonance potential remains below the target... 

Bardsley, J.N., Herzenberg, A. and Mandl, F. (1966). Vibrational excitation and dissociative attachment in the scattering of electrons by hydrogen molecules, Proc. Phys. Soc. (London) 89, 321-340. 

Chen, J.C.Y. (1966). Dissociative attachment in rearrangement electron collision with molecules, Phys. Rev. 148, 66-73. 

Domcke, W. and Miindel, C. (1985). Calculation of cross sections for vibrational excitation and dissociative attachment in HC1 and DC1 beyond the local complex potential approximation, J. Phys. B 18, 4491 1509. 

Miindel, C. and Domcke, W. (1984). Nuclear dynamics in resonant electron-molecule scattering beyond the local approximation model calculations on dissociative attachment and vibrational excitation, J. Phys. B 17, 3593-3616. 

Schneider, B.I., LeDourneuf, M. and Burke, P.G. (1979). Theory of vibrational excitation and dissociative attachment an R-matrix approach, J. Phys. B 12, L365-L369. 

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