Ternary Association Reaction of Vibrationally Cold N Ions in Ambient Helium.

The rate coefficients for the ternary association reaction of vibrationally cold N ions with N and He were measured in an afterglow plasma in the temperature range of 140-250 K: = (1.02 ± 0.39)(300/) × 10 cm s.

Recombination of vibrationally cold N2+ ions with electrons.

Recombination of vibrationally cold N2+ ions with electrons was studied in the temperature range of 140-250 K. A cryogenic stationary afterglow apparatus equipped with cavity ring-down spectrometer and microwave diagnostics was utilized to probe in situ the time evolutions of number densities of particular rotational and vibrational states of N2+ ions and of electrons. The obtained value of the recombination rate coefficient for the recombination of the vibrational ground state of N2+ with electrons is αv=0 = (2.

The reaction of O(S) ions with H, HD, and D at low temperatures: Experimental study of the isotope effect.

The reactions of the O ions in the S electronic ground state with D and HD were studied in a cryogenic 22-pole radio-frequency ion trap in the temperature range of 15 K-300 K. The obtained reaction rate coefficients for both reactions are, considering the experimental errors, nearly independent of temperature and close to the values of the corresponding Langevin collisional reaction rate coefficients. The obtained branching ratios for the production of OH and OD in the reaction of O(S) with HD do not change significantly with temperature and are consistent with the results obtained at higher collisional energies by other groups.

Dissociative recombination of NH ions with electrons in the temperature range of 80-350 K.

Recombination of NH ions with electrons was studied using a stationary afterglow with a cavity ring-down spectrometer. We probed in situ the time evolutions of number densities of different rotational and vibrational states of recombining NH ions and determined the thermal recombination rate coefficients for NH in the temperature range of 80-350 K. The newly calculated vibrational transition moments of NH are used to explain the different values of recombination rate coefficients obtained in some of the previous studies.

Towards state selective recombination of H under astrophysically relevant conditions.

We present studies on the thermalisation of H3+ ions in a cold He/Ar/H2 plasma at temperatures 30-70 K. We show that we are able to generate a rotationally thermalised H3+ ensemble with a population of rotational and nuclear spin states corresponding to a particular ion translational temperature. By varying the para-H2 fraction used in the experiment we are able to produce para-H3+ ions with fractional populations higher than those corresponding to thermodynamic values.

Stationary afterglow apparatus with CRDS for study of processes in plasmas from 300 K down to 30 K.

A cryogenic stationary afterglow apparatus equipped with a near-infrared cavity-ring-down-spectrometer (Cryo-SA-CRDS) for studies of electron-ion recombination processes in the plasma at temperatures 30-300 K has been designed, constructed, tested, and put into operation. The plasma is generated in a sapphire discharge tube that is contained in a microwave cavity. The cavity and the tube are attached to the second stage of the cold head of the cryocooler system, and they are inserted to an UHV chamber with mirrors for CRDS and vacuum windows on both ends of the tube.

Binary and ternary recombination of H2D(+) and HD2(+) ions with electrons at 80 K.

The recombination of deuterated trihydrogen cations with electrons has been studied in afterglow plasmas containing mixtures of helium, argon, hydrogen and deuterium. By monitoring the fractional abundances of H3(+), H2D(+), HD2(+) and D3(+) as a function of the [D2]/[H2] ratio using infrared absorption observed in a cavity ring down absorption spectrometer (CRDS), it was possible to deduce effective recombination rate coefficients for H2D(+) and HD2(+) ions at a temperature of 80 K. From pressure dependences of the measured effective recombination rate coefficients the binary and the ternary recombination rate coefficients for both ions have been determined.