Time-resolved HO₂ detection with Faraday rotation spectroscopy in a photolysis reactor

Abstract

Faraday rotation spectroscopy (FRS) employs the Faraday effect to detect Zeeman splitting in the presence of a magnetic field. In this article, we present system design and implementation of radical sensing in a photolysis reactor using FRS. High sensitivity (100 ppb) and time resolved in situ HO2 detection is enabled with a digitally balanced acquisition scheme. Specific advantages of employing FRS for sensing in such dynamic environments are examined and rigorously compared to the more established conventional laser absorption spectroscopy (LAS). Experimental results show that FRS enables HO2 detection when LAS is deficient, and FRS compares favorably in terms of precision when LAS is applicable. The immunity of FRS to spectral interferences such as absorption of hydrocarbons and other diamagnetic species absorption and optical fringing are highlighted in comparison to LAS.

NO2 Sensor Based on Faraday Rotation Spectroscopy Using Ring Array Permanent Magnets

“…The FRS signal is not disturbed by diamagnetic molecules such as CO 2 and H 2 O, so it has high species specificity. FRS utilizes magnetic circular birefringence (MCB), induced by Zeeman splitting in paramagnetic molecule’s absorption lines in an external magnetic field, to measure molecular concentrations . In the presence of an external magnetic field, the rotational–vibrational transition states of paramagnetic molecules are split into several sub-states due to the lifting of the degeneracy of the molecular energy levels (i.e., Zeeman splitting) .…”

Oxygen detection based on Faraday modulation spectroscopy and wavelength modulation spectroscopy: A comparison

“…In 2014, Liu et al used a widely tunable external cavity quantum cascade laser to detect the NO 2 by AC‐field FAMOS, and a detection sensitivity of ∼95 ppt was obtained in an averaging time of 300 s 20 . In 2018, Teng et al presented the system design and implementation of HO 2 detection in a photolysis reactor using FAMOS and the immunity of FAMOS to spectral interferences was proved 21 …”

“…In 2014, Liu et al used a widely tunable external cavity quantum cascade laser to detect the NO 2 by AC-field FAMOS, and a detection sensitivity of ∼95 ppt was obtained in an averaging time of 300 s. 20 In 2018, Teng et al presented the system design and implementation of HO 2 detection in a photolysis reactor using FAMOS and the immunity of FAMOS to spectral interferences was proved. 21 In this paper, we focus on the development and comparison of online O 2 detection based on FAMOS scheme and WMS scheme. The difference on sensor structure of the two schemes were present and the performance were experimentally evaluated.…”

Kinetics and Mechanism of the Singlet Oxygen Atom Reaction with Dimethyl Ether

“…Details of the experimental method have been explained previously. 13,29,30,33 In the present work, O( 1 D) atoms are generated by pulsed Nd:YAG laser photolysis (∼140 mJ/pulse, 0.25 Hz) at 266 nm of a gas mixture containing DME, oxygen, ozone, and helium. In situ laser light actinometry is performed to determine the photon flux F (photons cm −2 ) and the absolute concentration of O( 1 D).…”

“…Faraday rotational spectroscopy (FRS) has recently emerged, ,,, as a powerful method for the detection and quantitation of transient gas-phase paramagnetic species such as HO 2 . FRS provides interference-free detection of a molecule’s rovibrational transitions based on Zeeman splitting.…”