Overtone Transition 2ν1 of HCO+ and HOC+: Origin, Radiative Lifetime, Collisional Quenching.

We present spectra of the first overtone vibration transition of C-H/ O-H stretch (2ν1) in HCO+ and HOC+, recorded using a laser induced reaction action scheme inside a cryogenic 22 pole radio frequency trap. Band origins have been located at 6078.68411(19) and 6360.17630(26) cm-1, respectively. We introduce a technique based on mass selective ejection from the ion trap for recording background free action spectra. Varying the number density of the neutral action scheme reactant (CO2 and Ar, respectively) and collisional partner reactant inside the ion trap, permitted us to estimate the radiative lifetime of the state to be 1.53(34) and 1.22(34) ms, respectively, and the collisional quenching rates of HCO+(2ν1) with He, H2, and N2.

Dissociative recombination of N2H+ ions with electrons in the temperature range of 80-350 K.

Recombination of N2H+ 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 N2H+ ions and determined the thermal recombination rate coefficients for N2H+ in the temperature range of 80-350 K. The newly calculated vibrational transition moments of N2H+ are used to explain the different values of recombination rate coefficients obtained in some of the previous studies. No statistically significant dependence of the measured recombination rate coefficient on the buffer gas number density was observed.

Towards state selective recombination of H3+ 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. At 35 K, only the lowest rotational states of para and ortho H3+ are populated. This is the first step towards experimental studies of electron-molecular ion recombination processes with precisely specified quantum states at astrophysically relevant temperatures.