Investigating the photodissociation of H2O2 using frequency modulation laser absorption spectroscopy to monitor radical products

Kinetic study of the OH + ethylene reaction using frequency‐modulated laser absorption spectroscopy

“…The use of the OH vibrational overtone near 1.5 instead of the infrared fundamental near 3 exchanges a lower absorption cross section for a more convenient laser source and a light detector with better sensitivity and enough bandwidth to detect the RF beat signals of FM spectroscopy. 50 The recent demonstration of FM spectroscopy to monitor OH kinetics using the UV A-X transition 53 shares many of the features of the present work, with improved sensitivity associated with larger absorption cross sections, at the expense of a more difficult and complex UV probe laser source. The ability to measure and compare kinetic traces from multiple species using the same laser and detection technique, with only small changes in laser tuning can be an additional advantage for kinetic problems where simultaneous, calibrated measurements of OH and HO 2 may be desirable.…”

“…Compared to scanning a delay time in a laser photolysis, pulsed LIF method, an FM measurement using a continuous laser has the advantage of contributing a real‐time signal to an accumulating average at each shot of the pump laser. The use of the OH vibrational overtone near 1.5 μ instead of the infrared fundamental near 3 μ exchanges a lower absorption cross section for a more convenient laser source and a light detector with better sensitivity and enough bandwidth to detect the RF beat signals of FM spectroscopy . The recent demonstration of FM spectroscopy to monitor OH kinetics using the UV A‐X transition shares many of the features of the present work, with improved sensitivity associated with larger absorption cross sections, at the expense of a more difficult and complex UV probe laser source.…”

“…The OH radical kinetics reported here were measured inside a Herriott‐type slow flow reactor using FM laser absorption spectroscopy. This technique and apparatus have been described in detail elsewhere . Briefly, gas flows of nitric acid (HNO 3 ), C 2 H 4 and argon were regulated using calibrated mass flow controllers and flowed into a 2‐m glass Herriott‐type flow tube.…”

“…The recent demonstration of FM spectroscopy to monitor OH kinetics using the UV A‐X transition shares many of the features of the present work, with improved sensitivity associated with larger absorption cross sections, at the expense of a more difficult and complex UV probe laser source. The ability to measure and compare kinetic traces from multiple species using the same laser and detection technique, with only small changes in laser tuning can be an additional advantage for kinetic problems where simultaneous, calibrated measurements of OH and HO 2 may be desirable …”

“…FM spectroscopy offers several advantages as a detection method for kinetics studies of small reactive intermediates such as CN, 43 NH 2 , 44,45 CH 2 , 46,47 HCO, 48 and more recently, HO 2 , 49,50 C 2 H, 51,52 and OH. 50,53 Compared to more commonly applied laser-induced fluorescence methods for the investigation of OH reactions, 1,2,4,6,10,28 the absorption-based FM methods have a simpler dependence of the sensitivity on pressure and temperature conditions. The sensitivity of FM spectroscopy decreases slowly and predictably with increasing temperature and pressure, both due to the changing thermal population of the selected rotational state, and as Doppler broadening and pressure broadening change the absorption line shape and reduce the differential absorption of the radio frequency (RF) sidebands.…”