Collision molecules

LIF has been used to study state-selected ion-atom and ion-molecule collisions in gas cells. Ar reactions with N2 and CO were investigated by Leone and colleagnes in the 1980s [13, 14] and that group has... 

Several instniments have been developed for measuring kinetics at temperatures below that of liquid nitrogen [81]. Liquid helium cooled drift tubes and ion traps have been employed, but this apparatus is of limited use since most gases freeze at temperatures below about 80 K. Molecules can be maintained in the gas phase at low temperatures in a free jet expansion. The CRESU apparatus (acronym for the French translation of reaction kinetics at supersonic conditions) uses a Laval nozzle expansion to obtain temperatures of 8-160 K. The merged ion beam and molecular beam apparatus are described above. These teclmiques have provided important infonnation on reactions pertinent to interstellar-cloud chemistry as well as the temperature dependence of reactions in a regime not otherwise accessible. In particular, infonnation on ion-molecule collision rates as a ftmction of temperature has proven valuable m refining theoretical calculations. 

Bhowmik P K and Su T 1986 Tra]ectory calculations of ion-quadrupolar molecule collision rate constants J. Chem. Phys. 84 1432-4... 

Bernstein R B (ed) 1979 Atom-Molecule Collision Theory. A Guide for the Experimentalist New York Plenum)... 

Kaye J A and Kuppermann A 1988 Mass effect in quantum-mechanical collision-induced dissociation in collinear reactive atom diatomic molecule collisions Chem. Phys. 125 279-91... 

Kraijnovitch D J, Parmenter C S and Catlett D L Jr 1987 State-to-state vibrational transfer in atom-molecule collisions. Beams vs. bulbs Chem. Rev. 87 237-88... 

Flail R I and Read F FI 1984 Electron-Molecule Collisions ed I Shimamura and K Takayanagi (New York Plenum)... 

A partial wave decomposition provides the frill close-coupling quantal method for treating A-B collisions, electron-atom, electron-ion or atom-molecule collisions. The method [15] is siumnarized here for the inelastic processes... 

The close-coupling equations are also applicable to electron-molecule collision but severe computational difficulties arise due to the large number of rotational and vibrational channels that must be retained in the expansion for the system wavefiinction. In the fixed nuclei approximation, the Bom-Oppenlieimer separation of electronic and nuclear motion pennits electronic motion and scattering amplitudes f, (R) to be detemiined at fixed intemuclear separations R. Then in the adiabatic nuclear approximation the scattering amplitude for ... 

Baer M 1975 Adiabatic and diabatic representations for atom-molecule collisions treatment of the collinear arrangement Chem. Rhys. Lett. 35 112... 

In many ion-atom and ion-molecule collisions, one is often only interested in the projections on various charge states, which can be given a very simple treahnent. The Thouless determinant at separation of the two product fragments can be expressed as... 

When Che diameter of the Cube is small compared with molecular mean free path lengths in che gas mixture at Che pressure and temperature of interest, molecule-wall collisions are much more frequent Chan molecule-molecule collisions, and the partial pressure gradient of each species is entirely determined by momentum transfer to Che wall by mechanism (i). As shown by Knudsen [3] it is not difficult to estimate the rate of momentum transfer in this case, and hence deduce the flux relations. 

Since ions and neutral molecules are formed close together in an API source, many ion/molecule collisions occur as in Cl, and so the ion evaporation process also has impressed upon it the characteristics of Cl. Therefore, API is usually thought to involve a mix of ion evaporation and chemical ionization. 

The cold plasmas tend to be unstable, are sometimes difficult to maintain, and provide ion yields that are less than those of the hot plasmas. To obviate the difficulties of the interfering isobaric molecular ions from hot plasmas, it has been found highly beneficial to include a collision cell (hexapole see Chapter 22) before the mass analyzer itself. This collision cell contains a low pressure of hydrogen gas. lon/molecule collisions between the hydrogen and, for example, ArO+... 

Alternatively, ions of any one selected m/z value can be chosen by holding the magnetic field steady at the correct strength required to pass only the desired ions any other ions are lost to the walls of the instrument. The selected ions pass through the gas cell and are detected in the singlepoint ion collector. If there is a pressure of a neutral gas such as argon or helium in the gas cell, then ion-molecule collisions occur, with decomposition of some of the selected incident ions. This is the MS/MS mode. However, without the orthogonal TOF section, since there is no further separation by m/z value, the new ions produced in the gas cell would not be separated into individual m/z values before they reached the detector. Before the MS/MS mode can be used, the instrument must be operated in its hybrid state, as discussed below. 

To consider the effects of ion/molecule collisions on the trajectory of an ion, it is useful to consider ... 

Overall Effects of lon/Molecule Collisions and the Gse of Ion Transmission Guides... 

Additional ionization occurs by collision between the ions and other neutral species (ion/molecule collision see Chapter 1). Unless special steps are taken (see Chapters 8 and 11 ), the ions formed do not fragment, so little or no structural information is obtained. However, the lack of fragmentation does mean that good relative molecular mass data can be obtained. The assembly of ions formed by ion... 

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