The kinetics of the metathetical reaction of phenyl radical with methane has been studied theoretically and experimentally. The rate constants determined by two complementary methods, pyrolysis/Fourier transform infrared spectrometry and pulsed laser photolysis/mass spectrometry in the temperature range 600-980 K, give the Arrhenius equation: k 1 ) 10 12.78 ( 0.13 exp[(-6201 ( 225)/T] cm 3 /(mol s). At the best theoretical level employed (G2M(CC,MP2)), the barrier for the reaction at 0 K is E 1 0 ) 9.3 kcal/mol. The rate constant k 1 calculated from theoretical molecular parameters fits experimental data if the barrier height is increased to 10.5 kcal/mol. The fitted barrier is well within the 2-3 kcal/mol accuracy of the G2M method for the present open-shell, seven-heavy-atom system. Because of the relatively high reaction barrier and the predicted high imaginary frequency (1551 cm -1 ), tunneling corrections resulted in a significant enhancement in the calculated rate constant, 150% at 500 K and 7% at 2000 K. The theoretical result also correlates well with recently reported shock-tube data measured in the temperature range 1050-1450 K by UV absorption spectrometry. Kinetic analysis of the toluene formation data obtained from the photolysis of acetophenone without and with added H 2 and CH 4 gave the rate constant for the recombination of CH 3 and C 6 H 5 , k 2 ) (1.38 ( 0.08) × 10 13 exp [-(23 ( 36)/T] cm 3 /(mol s) for the temperature range 300-980 K.

The absolute bimolecular rate constants for the reactions of C 6 H 5 with 2-methylpropane, 2,3-dimethylbutane and 2,3,4-trimethylpentane have been measured by cavity ringdown spectrometry at temperatures between 290 and 500 K. For 2-methylpropane, additional measurements were performed with the pulsed laser photolysis/mass spectrometry, extending the temperature range to 972 K. The reactions were found to be dominated by the abstraction of a tertiary C-H bond from the molecular reactant, resulting in the production of a tertiary alkyl radical:

Photoelectron spectroscopy (PES), thermal programmed desorption (TPD) studies, and scanning tunneling microscopy (STM) investigated the interaction and chemistry of CH 3 (generated by the thermal cracking of azomethane) on Si/Cu(100). Si was deposited on Cu(100) by the thermal decomposition of SiH 4 at 420 K. STM of adsorbate-free Si/Cu(100) at a less than saturation coverage of Si revealed a surface that contained large domains of a Cu 2 Si structure. These Cu 2 Si domains coexisted with regions that were believed to be lower in fractional Si coverage. TPD results showed that (CH 3 ) 3 SiH desorbed near 200 K from CH 3 /Si/Cu-(100) prepared with a low Si concentration. With increasing Si concentration a (CH 3 ) 3 SiH desorption state appeared near 420 K, in addition to the 200 K state. The two observed TPD states of (CH 3 ) 3 SiH at 200 and 420 K were believed to be due to the thermal reaction of CH 3 with the low Si density and high Si density (i.e., Cu 2 Si) regions, respectively. At a saturation coverage of Si, when the well ordered Cu 2 Si phase covered the surface, only the 420 K peak was present during CH 3 /Si/Cu(100) TPD. Results also suggested that (CH 3 )-Si and possibly some (CH 3 ) 2 Si intermediates predominated on the surface below room temperature, and (CH 3 ) 3 -Si species were formed on the surface only at temperatures between 250 and 390 K. Surface hydrogen needed for the final evolution of (CH 3 ) 3 SiH was generated from methyl groups at temperatures above 390 K on the Si-saturated Cu(100). † Part of the special issue "Gabor Somorjai Festschrift".