Collisional damping

Hashimoto, Y., Waki, I., Yoshinari, K., Shishika, T., and Terui, Y. (2005). Orthogonal trap time-of-flight mass spectrometer using a collisional damping chamber. Rapid Commun. Mass Spectrom. 19 221-226. 

It is also expected that reactive collisions may diminish the effects of collisional damping of the z-oscillation. An unreactive collision removes energy from the z-mode oscillation so that the ion contributes more signal current at its original cyclotron frequency whereas a reactive collision removes an ion from a reactant population giving a true indication of the loss from the original population. The loss rate from the reactant population for ions of z-oscillation, Az, is proportional to the density of reactant ions of amplitude Az. Thus, for very reactive ions, no change in sensitivity due to collisional relaxation is expected. 

The simplest model of charge transport in delocalized bands is the Drude model, which assumes the carriers are free to move under the inhuence of an applied electric held, but subject to collisional damping forces. Note that the scattering centers are not the nuclei of the background material, but rather phonons (lattice vibrahons) or impurities. A statistical equahon for estimahng the mean drift velocity of the carriers in the direction of the electric held may be written as... 

To understand the information conveyed by an ICR signal, one has to solve the equation of motion of an ion under ICR conditions. The effect of collisions on the energy absorption of ions in the ICR cell is described by the Lorentz equation with the inclusion of a term for collisional damping ... 

B. Glushko, B. Kryzhanovsky Radiative and collisional damping effects on efficient population transfer in a three-level system driven by two delayed laser pulses, Phys. Rev. A 46 (1992) 2823. 

Fig. 1. Spectral decomposition of the Hamiltonian in the natural distinct subsets of states of the system Hum represents the molecular excitations, the one-photon continua, and Hpp the thermal bath of the colliding perturbers. Also indicated are the coupling terms responsible for the radiative and collisional damping processes.

Under general circumstances, where both radiative and collisional damping processes must be considered, the molecular resonances are then represented by the adjoint resonant functions v> and [Pg.291]

Here ylf = y(,v is the collisional damping constant, obtained from Eq. (42). Since yt is proportional to the gas pressure p... 

Here, the first term accounts for free coherent evolution of the excitations under the Hamiltonian given by Eq. (11). The second term describes relaxation through radiative and collisional damping of the molecular excited states, as indicated in Section II,A. The damping operators anmatrix elements are given by Eqs. (25) and (42). The final term represents the initial excitation process discussed above, corresponding to unit impulse operation of the light source (AT very small). 

The rate equations (147) and (148), which account for all the previously derived dynamical features of creation and evolution of the molecular excitations, are useful because they establish a connection with the standard Liouville equation formalism for rate processes in quantum statistical systems. It should be noted that they are submitted to the same assumptions as the treatment in Section II,A of the molecular resonant states. Collisional damping is described in the framework of impact approximation and weak... 

Therefore, eoupling of the radiant state s> with the complex nonradiant manifold, when treated statistically, gives rise to an increase of homogeneous broadening, with a corresponding decrease of the lifetime of this zero-order state. The intramolecular radiationless damping constant yj" is similar in nature to the radiationless collisional damping constant yr. 

Bandura, D.R., Baranov, V.I., Tanner, S.D. (2000) Effect of collisional damping and reactions in a dynamic reaction cell on the precision of isotope ratio measurements. Journal of Analytical Atomic Spectrometry, 15, 921-928. 

Collisional damping in a collision/reaction cell provides a significant improvement in the isotope ratio precision [98, 99]. This effect is created by pressurizing the cell with a nonreactive collision gas, typically Ne. As a result, ions extracted from the ICP at slightly different moments in time are admixed in the cell, thereby damping the short-term variations in the ion beam to some extent. The effect of the use of Ne as a non-reactive collision gas on the isotope ratio precision observed in practice is illustrated in Figure 2.24. 

By using collisional damping, the isotope ratio precision obtained can be improved to values of approximately 0.05% RSD (under optimum conditions). This gain in isotope precision, however, comes at the cost of a more pronounced instrumental mass discrimination [100-103], caused by preferential collisional losses of the lighter nuclide (Figure 2.25). 

Effed of collisional damping in the dynamic reaction cell on the predsion... 

Krutchinsky, A. N., I. V. Chemushevich, V. L. Spicer, W. Ens and K. G. Standing. 1998. Collisional damping interface for an electrospray ionization time-of-flight mass spectrometer. J. Amer. Soc. Mass Spectrom. 9 569-79. 

Krutchinsky, A. N. Loboda, A. V. Spicer, V. L. Dworschak, R. Ens, W. Standing, K. G. Orthogonal injection of matrix-assisted laser desorption/ionization ions into a time-of-flight spectrometer through a collisional damping interface. Rapid Commun. Mass Spectrom. 1998, 12, 508-518. 

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