RESUMEN
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 = (2.95 ± 0.50) × 10-7(300/T)(0.28±0.07) cm3 s-1, while that for the first vibrationally excited state was inferred as αv=1 = (4 ± 4) × 10-8 cm3 s-1 at 250 K.
RESUMEN
The reactions of the O+ ions in the 4S electronic ground state with D2 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+(4S) with HD do not change significantly with temperature and are consistent with the results obtained at higher collisional energies by other groups. Particular attention was given to ensure that the O+ ions in the trap are in the ground electronic state.
RESUMEN
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. The temperature of the discharge tube can be made as low as 25 K. In initial test measurements, the discharge was ignited in He/Ar/H2 or He/H2 gas mixtures and the density of H3+ ions and their kinetic and rotational temperatures were measured during the discharge and afterglow. From the measured decrease in the ion density, during the afterglow, effective recombination rate coefficients were determined. Plasma relaxation was studied in He/Ar gas mixtures by monitoring the presence of highly excited argon atoms. The spectroscopic measurements demonstrated that the kinetic temperature of the ions is equal to the gas temperature and that it can be varied from 300 K down to 30 K.