Ion–polar neutral momentum transfer collision frequencies: A theoretical approach

Abstract

A simple statistical theory is proposed which gives quantitative values for ion–polar neutral momentum transfer collision frequencies. The calculated collision frequencies depend on the rotational temperature of the neutrals, the translational temperature of the ions and neutrals, the masses of the ion and neutral, and the ratio of the neutral dipole moment to the square root of the neutral polarizability. Agreement with available experimental collision frequencies is very good. The results are consistent with available experimental rate constants for exothermic proton transfer reactions. The effects of nonorbiting collisions and finite ion–neutral hard sphere radius are examined.

Ion mobilities in gaseous ammonia

“…Using the pD/ali2 appropriate to ammonia and interpolating from their Table 2 and calculated the weighted mean mobilities shown under the heading BR in column 10 of Table 3. The agreement with experimental mobilities is very good, as has been the case for the comparison of Barker and Ridge's collision density calculations with other data (8). Neglect of the repulsive hard sphere interaction does not seem to have caused serious error for the present conditions.…”

“…Barker and Ridge (8) have recently obtained normalized collision densities, ~n~/ n ( M , a ) '~~, by calculating directly the average energy of interaction for the ion and dipole, a procedure which differs froin that of Su and Bowers. Using the pD/ali2 appropriate to ammonia and interpolating from their Table 2 and calculated the weighted mean mobilities shown under the heading BR in column 10 of Table 3.…”

Gas-phase oon-molecule reactions of transition metal complexes: The effect of different coordination spheres on complex reactivity

“…In the case of DIEN-(fur) 2 , DIEN-(thio) 2 , and DIEN-(phen) 2 complexes, addition of the first acetonitrile is completed during the first 500 ms of the reaction, leaving no trace of the parent ion. To gather some insight into the dynamics of this process, we have used the average dipole orientation (ADO) theory to calculate collision rate constants (k ADO ) [72][73][74][75]. We calculate the ADO capture rate constants using the parametrization of ion/polar-molecule collision developed by Su and Chesnavich [76].…”

Linewidth Pressure Measurement: A New Technique for High Vacuum Characterization

“…However, CRAFTI techniques [9,16] offer a means of measuring collision cross sections in gases other than Ar, as well as their kinetic energy dependence in the appropriate energy range, so that more options should soon become available. In addition, Barker-Ridge theory [17] could be used to estimate cross sections for other combinations of ions and neutral collision gases, making LIPS measurements possible for a wider range of systems, with the caveat that some error will be introduced because the kinetic energies of the ions in these experiments are not thermal.…”

“…This is an attractive idea because it might enable measurement of pressures directly in the FTICR cell, without depending on ionization potential or requiring an ion current measurement. A similar approach that used Barker-Ridge theory [17] to estimate momentum transfer cross sections and determined pressures in the trapping cell from the rate of transient decay in a conventional ion cyclotron resonance mass spectrometer has been described previously [18]. However, that treatment assumed ion-molecule collisions at thermal energies, which will introduce some error because the ions comprising a coherently orbiting packet are always at kinetic energies much greater than thermal, and cross sections are kinetic energy-dependent [19].…”