Analogous temperature-sweep and angular distribution data were collected for Ar. The translational energy distribution of the hyperthermal Ar beam is shown in Figure ; it had an average translational energy of 773 kJ mol -1 and an energy width (fwhm) of 76 kJ mol with θi = 45°. The potential long-term drift was mitigated with one "round trip" by varying θf from lowest to highest first, then from highest to lowest. The two TOF distributions collected at each θf were then added together. The total number of beam pulses corresponding to each TOF distribution collected for a given θf at m/z = 40 was 500.