Optoacoustic Lead-Salt Diode Laser Detection of Trace Species in a Flow System

An experimental setup for kinetic and product studies in a flow system has been developed. For detection, a nonresonant optoacoustic technique combined with a tunable lead-salt diode laser has been employed. The performance of the system was tested on ammonia in argon, and a detection limit (S/N = 2) of 8 × 1012 molecules cm−3 (corresponding to 320 ppb at atmospheric pressure) was obtained at a pressure of about 7 kPa when frequency modulation was employed. At 1.5 kPa the detection limit was about 2 × 1014 molecules cm−1. With a multipass cell the sensitivity was increased by a factor of four.