Laser-induced fluorescence technique to monitor H2S (PR 16023)

A means for detecting H2S at the 0.1 ppM level via laser induced fluorescence (LIF) was investigated. Because the upper electronic states of H2S are repulsive, it is necessary to use a two laser pump probe technique. The first laser (ArF, 193 nm) photodissociates H2S into HS and H. Subsequently, a probe dye laser is used to pump the HS ground state radicals to the state from which the radicals then fluoresce. This fluorescence signal can be related back to the H2S concentration prior to dissociation and thus affords a real time diagnostic for the species of interest. The quenching rate constants for DS (A state) quenching have been measured for the major constituents present in a gasifier. These data permit us to predict the fate of HS quenching. The quenching rate constants for HS cannot be measured directly. A correlation of the HS fluorescence signal with H2S concentration was made.