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Abstract: A new experimental set-up has been developed for studying astrochemically relevant collisions between small neutral carbon molecules Cn (n=1–3) and stored ions. The ions are confined for seconds in a ring electrode trap (RET) the temperature of which can be varied over a wide range (presently 80–600K). There they interact with an effusive carbon beam, which is produced via high-temperature vaporization of a carbon rod. Due to the accessible temperature range and other features of the set-up, rate coefficients can be measured, which are of importance for understanding the chemistry occurring in the outflow of stars, the formation of hydrocarbons in stellar atmospheres, and the interaction of the stored product ions with radiation. Results are reported for the interaction of stored D3+ with hot Cn. The D+ transfer dominates over all other exothermic product channels for n=1–3. The reaction rate coefficients measured for forming CnD+ are almost a factor two smaller than values presently used in astrophysical models. Another important class of reactions concerns the growth of pure carbon chains via associative Cm++Cn collisions. First results indicate that the rate coefficients are slower than generally assumed in models. Due to the weak signal, only rough limits can be reported. For future studies, the number density of carbon penetrating the trap must be increased. This and the planned extension of the temperature range is briefly discussed in the outlook. [Copyright &y& Elsevier]

Reactions of methane cations, CH4+, with H2, HD and D2 have been studied in a variable temperature 22-pole ion trap from room temperature down to 15 K. The formation of CH5+ in collisions with H2 is slow at 300 K, but it becomes faster by at least one order of magnitude when the temperature is lowered to 15 K. This behavior is tentatively explained with a longer complex lifetime at low temperatures. However, since tunneling is most probably not responsible for product formation, other dynamical or statistical restrictions must be responsible for the negative temperature dependence. In collisions of CH4+ with HD, the CH5+ product ion (68% at 15 K) prevails over CH4D+ (32%). Reaction of CH4+ with D2 is found to be much slower than with H2 or HD. The rate coefficient for converting CH4+ into CH3D+ by H–D exchange has been determined to be smaller than 10−12 cm3/s, indicating that scrambling in the CH6+ complex is very unlikely. [Copyright &y& Elsevier]

We present results of Stark shift measurements for He I 706.522 nm (1s2p 3 P 2 0 –1s3s 3 S 1 and 1s2p 3 P 1 0 –1s3s 3 S 1 ) lines using newly constructed pulsed arc generated at the pressure of two hundreds of milibars of helium with small admixture of hydrogen. Plasma electron number density in the range (0.5–7.0)×10 23 m −3 was measured from the wavelength separation between the allowed He I 447.1 nm (2p 3 P 0 –4d 3 D) line and its forbidden component (2p 3 P 0 –4d 3 F 0 ), while the electron temperature in the range (15,000–20,000) K was determined from the relative intensities of Si II lines using the Boltzmann plot technique. New Stark shift measurement technique was demonstrated using line shape recording of several He I lines. The shift results for He I 706.522 nm line so favorably compare with earlier lower density experimental data that best fit formula is recommended for plasma diagnostic purposes. [ABSTRACT FROM AUTHOR]

Stark widths and shifts of 13 Ar II spectral lines in the visible part of spectrum were measured. Spectral lines were emitted from pulsed wall stabilized Ar arc plasma under atmospheric pressure. Profiles were recorded at plasma electron densities of 1.3×10 23 m −3 and 1.6×10 23 m −3 and plasma electron temperatures of 13,400 K and 14,200 K respectively. Obtained results are compared with other experimental results as well as with theoretical values. The analysis of the experimental and theoretical data is given as well. [ABSTRACT FROM AUTHOR]