2:45 PM - 3:00 PM
[PCG19-11] A novel laboratory approach to studying photochemistry of liquid organic interfaces
★Invited Papers
Surface and interfacial photochemistry of organic molecules have become increasingly of interest in the field of terrestrial atmospheric chemistry. In the Earth, surface-active organics such as fatty acids are ubiquitous, which cover the surfaces of oceans, lakes, cloud and fog droplets, and atmospheric aerosol particles. Rossignol et al. recently reported that, although fatty acids are believed to be photochemically inert in the actinic region, complex volatile organic compounds are produced during illumination of an air-water interface coated solely with a monolayer of nonanoic acid [CH3(CH2)7COOH] [1, 2]. The authors suggest that, when nonanoic acid is present in coatings at a water-air interface, it weakly absorbs ultraviolet light at wavelengths present in sunlight at Earth’s surface and yields hydroxyl (OH) and nonyl radicals.
This previous study emphasizes the requirement to understand the elementary processes of photochemistry occurring on liquid organic interfaces. However, direct detection of primary photoproducts represented by radicals is technically challenging. Conventional methods suitable for detection of radicals such as resonance enhanced multi photon ionization (REMPI) generally require ultrahigh-vacuum conditions (10-4 Pa for REMPI), whereas liquid organic compounds intrinsically have high vapor pressures (1 Pa for nonanoic acid), which prevents us from performing direct detection of radicals.
We are currently working on developing a new type of experimental setup to study the interface photochemistry of liquid organic with high vapor pressure. Laser-induced fluorescence is employed to detect primary photoproducts desorbing from the liquid organic interface. In this talk, we show preliminary results that direct photolysis of liquid nonanoic acid [CH3(CH2)7COOH] leads to the formation of OH radicals. The present technique can be also useful to study the chemistry in planetary atmospheres, as well as high pressure environments in protoplanetary disks.
Figure caption. Photographs of the new experimental setup for studying photochemistry of liquid organic interfaces.
[1] Rossignol et al., Science 353, 699 (2016).
[2] Vaida. Science 353, 650 (2016).
This previous study emphasizes the requirement to understand the elementary processes of photochemistry occurring on liquid organic interfaces. However, direct detection of primary photoproducts represented by radicals is technically challenging. Conventional methods suitable for detection of radicals such as resonance enhanced multi photon ionization (REMPI) generally require ultrahigh-vacuum conditions (10-4 Pa for REMPI), whereas liquid organic compounds intrinsically have high vapor pressures (1 Pa for nonanoic acid), which prevents us from performing direct detection of radicals.
We are currently working on developing a new type of experimental setup to study the interface photochemistry of liquid organic with high vapor pressure. Laser-induced fluorescence is employed to detect primary photoproducts desorbing from the liquid organic interface. In this talk, we show preliminary results that direct photolysis of liquid nonanoic acid [CH3(CH2)7COOH] leads to the formation of OH radicals. The present technique can be also useful to study the chemistry in planetary atmospheres, as well as high pressure environments in protoplanetary disks.
Figure caption. Photographs of the new experimental setup for studying photochemistry of liquid organic interfaces.
[1] Rossignol et al., Science 353, 699 (2016).
[2] Vaida. Science 353, 650 (2016).