Deposition Rate Monitor for Matrix Isolation Studies of High Temperature Species

Abstract

In matrix isolation studies of high temperature species the relative deposition rates of the host and guest largely determine the degree of isolation, an important consideration for studies of many molecules which tend to react or to polymerize in concentrated matrices. The rate of deposition of the matrix gas is conveniently measured by flowmeter, but the guest deposition rate is not so easily obtained. For effusion from a Knudsen cell, the rate can be estimated from the vapor pressure of the species at the effusion temperature. Often, however, such vapor pressure data are unavailable, and, moreover, absolute temperature measurements are not trivial at high temperatures. In addition, even at a fixed temperature we have observed marked decreases in rates of deposition with time because of internal migration of salts to the cooler regions of the Knudsen cell. Such factors clearly demonstrate the need for a more direct monitor of the effusion rate.