Pressure-induced dissociation

The NO+ ions must eventually be neutralized to produce some stable excited states since Nj < 1 is obtained. An increase of pressure indicates the occurrence of the pressure induced dissociation... 

Guy, H. I., Schmidt, B., Herve, G., and Evans, D. R. (1998). Pressure-induced dissociation of carbamoyl-phosphate synthetase domains. The catalytically active form is dimeric. J Biol Chem., 273, 14172-14178. 

Figure 9. Pressure induced dissociation of the GLN-CPS.B dimer. The uncrosslinked dimer (open spheres) was subjected to 1500 bar (- -) or incubated at atmospheric pressure (- -). The crosslinked dimer (filled spheres) was also subjected to 1500 bar (- -) or atmospheric pressure (-0-).

By introducing a collision gas into Q2, collision-induced dissociation (CID) can be used to cause more ions to fragment (Figure 33.4). For example, with a pressure of argon in Q2, normal ions (mj ) collide with gas molecules and dissociate to give mj ions. CID increases the yield of fragments compared with natural formation of metastable ions without induced decomposition. 

CO2, N2 and N2O production as a function of the catalyst potential, UWR> obtained at 62IK for fixed inlet pressures of NO and CO. A sharp increase in reaction rate and product is observed as the catalyst potential is reduced below 0 V, i.e., upon Na supply to the Pt catalyst. The selectivity to N2, Sn2, is enhanced from 17% to 62%. This dramatic enhancement in catalytic performance is due to (a) enhanced NO vs CO chemisorption on Pt with decreasing potential and (b) Na-induced dissociation of chemisorbed NO. 

Processes accompanied by a decrease in volume, such as C—C bond formation, in which the distance between two carbon atoms decreases from the van der Waals distance of ca 3.6 A to the bonding distance of ca 1.5 A, are accelerated by raising the pressure and equilibria are shifted toward the side of products (AV < 0, AV < 0). The reverse reaction, a homolytic bond cleavage, leads to an increase in volume (AV / > 0, AV > 0). Pressure induces a deceleration of such a process and a shift in equilibrium toward the side of reactants. However, in an ionization, such as an ionic dissociation, the attractive interaction between the ions generated and the solvent molecules leads to a contraction... 

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... 

In spite of the fact that in alkali vapors, which contain about 1 % diatomic alkali-molecules at a total vapor-pressure of 10 torr, the atoms cannot absorb laser lines (because there is no proper resonance transition), atomic fluorescence lines have been observed 04) upon irradiating the vapor cell with laser light. The atomic excited states can be produced either by collision-induced dissociation of excited molecules or by photodissociation from excited molecular states by a second photon. The latter process is not improbable, because of the large light intensities in the exciting laser beam. These questions will hopefully be solved by the investigations currently being performed in our laboratory. 

Our group has termed this process zero pressure thermal-radiation-induced dissociation (ZTRID). 

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