HDS

Fig. X-12. Advancing and receding contact angles of various liquids [water (circles), Gly = glycerol (squares), Form = formamide (diamonds), EG = ethylene glycol (circles), BN = abromonapthalene (squares), BCH = bicyclohexyl (diamond), HD = hexadecane (circles)] on monolayers of HS(CH2)i60R having a range of R groups adsorbed on gold and silver (open and filled symbols respectively). (From Ref. 171.)...

Process 2, the adsorption of the reactant(s), is often quite rapid for nonporous adsorbents, but not necessarily so it appears to be the rate-limiting step for the water-gas reaction, CO + HjO = CO2 + H2, on Cu(lll) [200]. On the other hand, process 4, the desorption of products, must always be activated at least by Q, the heat of adsorption, and is much more apt to be slow. In fact, because of this expectation, certain seemingly paradoxical situations have arisen. For example, the catalyzed exchange between hydrogen and deuterium on metal surfaces may be quite rapid at temperatures well below room temperature and under circumstances such that the rate of desorption of the product HD appeared to be so slow that the observed reaction should not have been able to occur To be more specific, the originally proposed mechanism, due to Bonhoeffer and Farkas [201], was that of Eq. XVIII-32. That is. 

Figure A2.2.2. The rotational-vibrational specific heat, C, of the diatomic gases HD, HT and DT as a fiinction of temperature. From Statistical Mechanics by Raj Pathria. Reprinted by pennission of Butterwortii Heinemann.

Rettner C T and Auerbach D J 1996 Quantum-state distributions for the HD product of the direct reaction of H(D)/Cu(111) with D(H) incident from the gas phase J. Chem. Phys. 104 2732... 

Schnieder L, Seekamp-Rahn K, Wede E and Welge K H 1997 Experimental determination of quantum state resolved differential cross sections for the hydrogen exchange reaction H -r D2 -> HD -r D J. Chem. Phys. 107 6175-95... 

Zhang J Z H and Miller W H 1989 Quantum reactive scattering via the S-matrix version of the Kohn variational principle—differential and integral cross sections for D + Hj —> HD + H J. Chem. Phys. 91 1528... 

Gray S K and Balint-Kurti G G 1998 Quantum dynamics with real wave packets, including application to three-dimensional (J = 0)D + H2 HD + H reactive scattering J. Chem. Phys. 108 950... 

The electronic wave functions of the different spin-paired systems are not necessarily linearly independent. Writing out the VB wave function shows that one of them may be expressed as a linear combination of the other two. Nevertheless, each of them is obviously a separate chemical entity, that can he clearly distinguished from the other two. [This is readily checked by considering a hypothetical system containing four isotopic H atoms (H, D, T, and U). The anchors will be HD - - TU, HT - - DU, and HU -I- DT],... 

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