Activated dissociation

The activated dissociation of H2 (D2) on Cu(l 11) and other single crystal Cu surfaces has played a special role in the development of reactive gas-surface dynamics. Early experiments and theory by Cardillo and collaborators [217-219] first demonstrated the power of molecular beam techniques to probe activated adsorption and the theoretical methodology developed by them (6D quasi-classical dynamics on a model PES) only differs from modem treatments in the use of DFT based PES. 

They also first proposed the use of detailed balance to relate dissociative adsorption to associative desorption. In hindsight, both the experiments and the PES derived by them to fit the experiments were in significant quantitative error, but this in no way minimizes the major contribution of this early work to the development of reactive gas-surface dynamics. 

A key new element in the associative desorption experiments is the ability to probe different rotational states and rotational alignment. Assuming that the dominant effect of rotation is to make the thresholds dependent upon rotational state, 

Since both adsorption and desorption experiments have been performed, it is possible to determine if the experiments satisfy detailed balance and probe the same phase space. They do not, probably because sticking at low , is dominated by dissociation at the steps while associative desorption at higher 0N principally measures desorption from the terraces [244]. There is also ambiguity as to whether energy loss to the lattice and e-h pairs is the same in the two different types of experiments. 

State-resolved inelastic scattering for a wide range of incident conditions ( ), d,) are measured for this system by combining molecular beam techniques with (2 + 1) ion TOF REMPI detection of the scattered molecules [58]. Energy transfer parallel to the surface is measured from the Doppler broadening of the REMPI spectra. Trapping 

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Direct dissociation reactions are affected by surface temperature largely tlirough the motion of the substrate atoms [72]. Motion of the surface atom towards the incoming molecule mcreases the likelihood of (activated) dissociation, while motion away decreases the dissociation probability. For low dissociation probabilities, the net effect is an enliancement of the dissociation by increasing surface temperature, as observed in the system 02/Pt 100]-hex-R0.7° [73]. 

Rettner C T, Schweizer E K and Stein H 1990 Dynamics of chemisorption of N2 on W(100) Precursor-mediated and activated dissociation J. Chem. Phys. 93 1442... 

U ] Rettner C T and Stein H 1987 Effect of the translational energy on the chemisorption of N2 on Fe(111) activated dissociation via a precursor state Phys. Rev. Lett. 59 2768... 

Beebe T P, Goodman D W, Kay B D and Yates J T Jr 1987 Kinetics of the activated dissociation adsorption of methane on low index planes of nickel single crystal surfaces J. Chem. Phys. 87 2305... 

Collision-induced dissociation (or decomposition), abbreviated CID. An ion/neutral process wherein the (fast) projectile ion is dissociated as a result of interaction with a target neutral species. This is brought about by conversion during the collision of part of the translational energy of the ion to internal energy in the ion. The term collisional-activated dissociation (or decomposition), abbreviated CAD, is also used. 

Collision-activated dissociation (CAD) The same process as collision-induced dissociation (CID). 

In most systems the fraction of the active dissociated polymers [P, Li], is very low, and then the following approximation is justified... 

Clearly, the sticking coefficient for the direct adsorption process is small since a considerable amount of entropy is lost when the molecule is frozen in on an adsorption site. In fact, adsorption of most molecules occurs via a mobile precursor state. Nevertheless, direct adsorption does occur, but it is usually coupled with the activated dissociation of a highly stable molecule. An example is the dissociative adsorption of CH4, with sticking coefScients of the order 10 -10 . In this case the sticking coefficient not only contains the partition functions but also an exponential... 

J. Shen and A. S. Al-Saeed. Study of oil field chemicals by combined field desorption/collision-activated dissociation mass spectrometry via linked scan. Ana/y Chem, 62(2) 116-120, 1990. 

The experimental evidence, first based on spectroscopic studies of coadsorption and later by STM, indicated that there was a good case to be made for transient oxygen states being able to open up a non-activated route for the oxidation of ammonia at Cu(110) and Cu(lll) surfaces. The theory group at the Technische Universiteit Eindhoven considered5 the energies associated with various elementary steps in ammonia oxidation using density functional calculations with a Cu(8,3) cluster as a computational model of the Cu(lll) surface. At a Cu(lll) surface, the barrier for activation is + 344 k.I mol 1, which is insurmountable copper has a nearly full d-band, which makes it difficult for it to accept electrons or to carry out N-H activation. Four steps were considered as possible pathways for the initial activation (dissociation) of ammonia (Table 5.1). 

Diarylfuroxans were found to give diarylacetylenes upon irradiation at 254 nm (Equation 9, Table 2). Cyclobutaphenanthrenes were also obtained when reaction was carried out in the presence of alkenes (Equation 10). The acetylenic derivative is supposed to arise by loss of (NO)2 from a diazete-iV,iV-dioxide. Unimolecular and collision-activated dissociation studies by tandem mass spectrometry also support the loss of (NO)2 from diarylfuroxans molecular ions <1997T17407>. 

DGE a AC AMS APCI API AP-MALDI APPI ASAP BIRD c CAD CE CF CF-FAB Cl CID cw CZE Da DAPCI DART DC DE DESI DIOS DTIMS EC ECD El ELDI EM ESI ETD eV f FAB FAIMS FD FI FT FTICR two-dimensional gel electrophoresis atto, 10 18 alternating current accelerator mass spectrometry atmospheric pressure chemical ionization atmospheric pressure ionization atmospheric pressure matrix-assisted laser desorption/ionization atmospheric pressure photoionization atmospheric-pressure solids analysis probe blackbody infrared radiative dissociation centi, 10-2 collision-activated dissociation capillary electrophoresis continuous flow continuous flow fast atom bombardment chemical ionization collision-induced dissociation continuous wave capillary zone electrophoresis dalton desorption atmospheric pressure chemical ionization direct analysis in real time direct current delayed extraction desorption electrospray ionization desorption/ionization on silicon drift tube ion mobility spectrometry electrochromatography electron capture dissociation electron ionization electrospray-assisted laser desorption/ionization electron multiplier electrospray ionization electron transfer dissociation electron volt femto, 1CT15 fast atom bombardment field asymmetric waveform ion mobility spectrometry field desorption field ionization Fourier transform Fourier transform ion cyclotron resonance... 

The dissociation of gas-phase ions can be a guide to the structure of the ions. There are two ways to dissociate gas-phase ions, either by collision-induced dissociation (CID) sometimes termed collision-activation dissociation (CAD) or by photodissociation. In each method, a mass selected ion is dissociated and the fragment ion (often called a daughter ion) is measured the neutral fragment cannot be experimentally observed. 

CAD Collision-activated dissociation CID Collision-induced dissociation... 

Synonymous terms used Collisional activation (CA) and collision-activated dissociation (CAD). 

Gauthier, J.W. Trautman, T.R. Jacobson, D.B. Sustained Off-Resonance Irradiation for Collision-Activated Dissociation Involving FT-ICR-MS. CID Technique That Emulates Infrared Multiphoton Dissociation. Anal. Chim. Acta 1991,246,211-225. 

Smith, R.D. Loo, J.A. Baiinaga, C.J. Edmonds, C.G. Udseth, H.R. Colhsional Activation and Collision-Activated Dissociation of Large Multiply Charged Polypeptides and Proteins Produced hy ESI. J. Am. Soc. Mass Spectrom. 1990,1, 53-65. 

Conventional wisdom concerning thermal unimolecular reactions would seem to dictate that this must then be a Lindemann-type collisionally activated dissociation reaction scheme such as is in Equation (17). Application of the steady-state... 

Cadmium thiocyanates, 17 333-336 Cadmium trifluoroacetates, 17 25, 26 CAD spectra, see Collisionally activated dissociation spectra... 

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