Time-resolved time-of-flight mass spectrometry with molecular-pulse-probes for analysis of dynamic process in surface catalytic reactions in millisecond range (II)

A dynamic vacuum system for transient analyses of surface catalytic reaction equipped with four pulsed valves as molecular sources, a cryopump which has a huge pumping speed and a time-of-flight mass spectrometer (TOF) were developed. A simple linear TOF system was found to get sufficient signal intensity with the help of (1) employment of pulsed valves to supply sufficient amounts of gas molecules to the planar sample, (2) the geometrical design of the vacuum system including a three stages differential pumping vacuum system, and (3) the background noise subtraction by data processing. The features in instrumentation, data acquisition/processing are described with a typical example of the NO + H2 reaction over a Pt film (673 K), where a H2 gas pulse injection was followed by a NO gas pulse injection just after a 10 ms interval and the change of the reaction products such as N2 and H2O were detected in ms range.