Photothermal deflection spectroscopy in cryogenic liquids and its application to quantitative atmospheric trace analysis

Abstract

An evaluation is presented of quantitative trace concentration measurement using liquefied samples of gas. The trace molecule of interest in a mixture of molecules is excited using a tunable IR laser. Following excitation, the vibrationally excited molecules are deactivated rapidly in collisions with the solvent. This leads to local solvent heating and a local density gradient. These are detected using the photothermal deflection of a He–Ne probe laser beam. Tests have been made using SF ₆ , which has been quantitatively detected down to 10 parts per trillion in liquid argon. The application of this technique to the analysis of atmospheric samples is discussed.