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Using the combination of a linear 22-pole ion trap (22 PT) and a coaxial beam of hydrogen atoms, H abstraction from CH x + (x=1, 4 and 5) has been studied. The temperature of the trap, T 22 PT, can be varied between 10 K and 300 K. The velocity distribution of the neutral target beam can be changed by cooling the accommodator (T ACC=10–300 K) and using the focusing features of one or two hexapole magnets. The resulting velocity distributions are characterized by time-of-flight measurements. With the same setup, reactions of mass selected stored ions with a cold effusive beam of H2 molecules have been measured with the discharge turned off. At temperatures of interstellar space, H-abstraction from CH+ is efficient. CH4 + reacts five times faster with H than with H2 at 50 K. In contradiction to ab initio calculations and to the established proton affinity of methane, CH5 + is slowly destroyed in collisions with H in our trap, even at 10 K. Some first results for collisions between CH x + and D atoms are reported. For x=1, H–D exchange is quite efficient, even though it is in competition with the exothermic abstraction reaction. For x=4, H-abstraction, i.e. formation of HD molecules, dominates. Deuteration of CH5 + is measured to be very slow.

This progress report presents recent advances in developing a versatile technique for investigation of collisions of ions with open shell neutral intermediates. Combination of a 22-pole ion trap with a beam of H atoms allows accurate determination of rate coefficients at temperatures between 10 K and 300 K. New experimental results on hydrogen abstraction in collisions of CH + , CH 4 + and CH 5 + ions with H atoms are reported at temperatures between 10 K and 100 K. In the case of CH + and CH 4 + , large rate coefficients of 1.3 × 10-9 cm 3 s-1 and 6.0 × 10-10 cm 3 s-1 have been obtained at 50 K. CH + reacts with D atoms with a total rate coefficient of 2.4 × 10-9 cm 3 s-1 the branching ratio being 50 % for hydrogen abstraction and 50 % for atom exchange. For collisions of CH 5 + with H atoms rate coefficients of 9 × 10-12 , 1.3 × 10-11 , and 2.3 × 10-11 cm 3 s-1 have been determined at trap and nozzle temperatures of 10, 50, and 100 K, respectively. This indicates that this reaction is almost thermoneutral in contrast to thermodynamical data reported in the literature.

A new instrument has been developed which combines a rf ring electrode trap and a time-of-flight mass spectrometer ͑TOF-MS͒. The wide field free storage volume of such a trap enables the study of low temperature ion-molecule collisions; however it is not straightforward to match the nonlocalized ion cloud to the TOF-MS. For obtaining sufficient mass resolution, a special pulse sequence has been developed to transfer the ions from the whole trap volume to a small region in the vicinity of the exit electrode. Additional compression is achieved via buffer gas relaxation prior to extracting the ions. Using a linear flight path of 57 cm, a mass resolution of about 50 is routinely achieved. The mass range of the whole instrument, which is determined by the operating conditions both of the trap and the TOF-MS, has been estimated to be 3-700 u. The actual characteristics of the instrument such as mass range, resolution, and dynamical range have been determined and the results have been analyzed. As a typical application of the new instrument, the growth of (CO) n ϩ cluster ions is investigated at 80 K. The simultaneous detection of all masses of interest as a function of storage time allows one to follow in detail the kinetics of the reaction and loss processes involved. Limitations of the method are discussed together with ways to overcome them in an improved setup.