Measuring Photodissociation Product Quantum Yields Using Chemical Ionization Mass Spectrometry: A Case Study with Ketones

Abstract

Measurements of photolysis quantum yields are challenging because of the difficulties in measuring the first-generation photodissociation products, interference from other products or contaminants, sufficient photon fluxes and/or low absorption cross sections of the photolyte to make detectable amounts of products, and quantification of the photon flux. In the case of acetone (and other atmospherically relevant ketones) the uncertainty in the photolysis quantum yield creates uncertainty in the calculated OH radical and acyl peroxy nitrate production in the atmosphere. We present a new method for determining photodissociation product quantum yields by measuring acyl peroxy radicals (RC(O)O 2 ) produced in the photolysis of ketones in air using chemical ionization mass spectrometry (CIMS). We show good agreement of our CIMS method with previously published quantum yields of the acyl radical from photolysis of biacetyl and methyl ethyl ketone (MEK) at 254 nm. Additionally, we highlight the capabilities of this CIMS method through the measurement of photolysis branching ratios for MEK. We suggest future applications of CIMS (in the laboratory and field) to measure RC(O)O 2 and associated photolysis processes.

Model Evaluation of Secondary Chemistry due to Disinfection of Indoor Air with Germicidal Ultraviolet Lamps

“…UVC light is known to generate strong oxidants (e.g., OH radicals, and sometimes also O 3 depending on the wavelengths used), which can subsequently oxidize volatile organic compounds (VOCs) indoors and initiate organic radical chemistry in indoor air. , Energetic UVC photons can also directly photolyze many VOCs, such as peroxides , and carbonyls, , and generate organic radicals. This radical chemistry is thought to lead to further oxidation of indoor VOCs and the formation of oxygenated VOCs (OVOCs) and secondary organic aerosol (SOA), both of which may have negative health effects .…”

Virtual Issue on Photodissociation: From Fundamental Dynamics and Spectroscopy to Photochemistry in Planetary Atmospheres and in Space

“…Notably, the James Webb Space Telescope is now providing IR spectroscopic data on the compositions of the atmospheres of exoplanets outside our solar system. In addition to wavelength-dependent absorption cross-sections derived from spectroscopic studies, laboratory measurements can quantify the branching between competing photochemical pathways together with the associated photodissociation quantum yields, for which accurate new methods of determination have recently been proposed. , A combination of such data is needed in order to calculate rates of photolytic loss and production of reactive intermediates in environments such as the Earth’s atmosphere and the interstellar medium and, hence, to establish the influence of photochemical reactions on the chemistry of these regions. , …”

“…In addition to wavelengthdependent absorption cross-sections derived from spectro-scopic studies, laboratory measurements can quantify the branching between competing photochemical pathways 17 together with the associated photodissociation quantum yields, for which accurate new methods of determination have recently been proposed. 38,39 A combination of such data is needed in order to calculate rates of photolytic loss and production of reactive intermediates in environments such as the Earth's atmosphere and the interstellar medium and, hence, to establish the influence of photochemical reactions on the chemistry of these regions. 1,23 The photochemistry occurring in the Earth's troposphere and much of the stratosphere is driven by photodissociation at UV or visible wavelengths.…”

Model Evaluation of Secondary Chemistry due to Disinfection of Indoor Air with Germicidal Ultraviolet Lamps

“…3,18 UVC light is known to generate strong oxidants (e.g., OH radicals, and sometimes also O3 depending on the wavelengths used), 20 which can subsequently oxidize volatile organic compounds (VOCs) indoors and initiate organic radical chemistry in indoor air. 21,22 Energetic UVC photons can also directly photolyze many VOCs, such as peroxides 23,24 and carbonyls, 25,26 and generate organic radicals. This radical chemistry is thought to lead to further oxidation of indoor VOCs and the formation of oxygenated VOCs (OVOCs) and secondary organic aerosol (SOA), both of which may have negative health effects.…”