HIGH-TEMPERATURE OCTOPOLE ION GUIDE FOR MEASURING ABSOLUTE CROSS-SECTIONS OF ION-METAL ATOM REACTIONS

We describe in detail a high-temperature octopole/collision cell appar atus for studying ion-molecule reactions involving nonvolatile target species, including metals. The system can be operated at temperatures up to similar to 1200 K and features coaxially heated octopole rods an d a heated collision cell in which the vapor of a nonvolatile target m aterial is generated by evaporation from a bulk sample contained there in. The poles are heated independently of the cell and are maintained at a higher temperature Co prevent condensation of the sample on the p oles. This ensures a well characterized operating temperature that is necessary for absolute cross-section measurements. The apparatus desig n permits two independent methods for the determination of the target vapor density. The absolute Na+N-2(+) charge transfer cross section ha s been measured for collision energies in the range 0.1-2.25 eV. These results represent the first guided-ion beam measurement of an absolut e ion-metal atom reaction cross section, and are compared to earlier s tudies conducted with other methods. (C) 1997 American Institute of Ph ysics.