Ion trap technique in combination with photodetachment spectroscopy was used to study the thermalization of OH- in the temperature range of 50-200 K. The ions were trapped in a multipole radiofrequency trap and cooled by helium buffer gas.
The photodetachment spectra were recorded as a dependence of OH- losses in trap on frequency. The preliminary results show an excellent agreement between the OH- rotational temperature and the temperature of 22-pole trap in the studied temperature range.