This biennial Review summarizes much of particle physics. Using data from previous editions, plus 2778 new measurements from 645 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. Among the 108 reviews are many that are new or heavily revised including those on CKM quark-mixing matrix, Vud & Vus , Vcb & Vub , top quark, muon anomalous magnetic moment, extra dimensions, particle detectors, cosmic background radiation, dark matter, cosmological parameters, and big bang cosmology. A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: http://pdg.lbl.gov

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The photodissociation of 1,1-and 1,2-difluoroethylene (DFE) at 193 nm was studied by measuring product translational energy distributions, P(E T ), for the various product channels. The P(E T )'s are used to obtain information on the exit barriers, product internal energy, transition states, and the stability of intermediates in many of these channels. Significant differences in the P(E T )'s for three-centered elimination of HF to produce :CdCHF and four-centered elimination of HF to give HCtCF were observed. These were attributed to differences in the exit barriers and transition states for the two types of elimination. This is the first reported study of the three-and four-centered H 2 elimination pathways producing :CdCF 2 and FCtCF, respectively. Both reactions showed the presence of a small exit barrier. This work also gives the first detailed description of the H and F atomic elimination channels. The P(E T ) for primary H atom elimination indicates a simple bond rupture mechanism; the P(E T ) for secondary H atom elimination suggests that triplet product is formed. The P(E T )'s for F atom elimination indicate that • CHdCHF is more stable than • CFdCH 2 . Where appropriate, comparisons of the various DFE and ethylene photodissociation channels were made.