UCSD researchers use cold COAT to study photochemistry of ozonide anions
UCSD researchers use cold COAT to study photochemistry of ozonide anions lead image
The ozonide anion (O3¯) and superoxide (O2¯) and O¯ all play a role in mediating the free electron density in the ionosphere, impacting electromagnetic wave propagation and communication. The photodissociation of O3¯ couples the chemistry of these species, and it turns out that the photochemical reactions of O3¯ are extremely sensitive to internal vibrational excitation in a way that governs the production of O¯, O2¯ and excited neutral oxygen, O2(1Δg). Quenching this excitation and studying the ‘cold’ molecule is a continuous challenge, however, researchers at the University of California, San Diego coupled a cryogenic octopole accumulation trap (COAT) to their photoelectron-photofragment coincidence spectrometer to eliminate internal excitation. They presented their results in The Journal of Chemical Physics.
Lead researcher Robert Continetti explains that while cooling molecular ions has been accomplished previously, it was difficult to cool some high energy vibrational excitations. For that reason, the UCSD team added COAT to their unique spectrometer to study the photochemistry of ozonide anions without internal excitation.
Researchers trapped ions in COAT, then cooled them by buffer gas collisions, achieving a temperature of ∼10K which effectively ‘turned-off’ one of the dissociation channels. Continetti and his team also enhanced this dissociation channel by promoting collisional excitation of the ions and then trapping them for a short time. The researchers were surprised how sensitive the photochemistry of O3¯ was to internal excitation. Continetti says this is an important advance, opening the way to study larger, more difficult-to-cool molecular anions.
The paper states that the sensitivity of this dissociation channel to parent ion vibrational excitation makes it an ideal candidate for measuring how vibrational excitation of O3¯ and the photodissociation/autodetachment pathway are coupled, an important challenge for theoreticians seeking to explain such phenomena from first principles.
Source: “Internal energy dependence of the photodissociation dynamics of O3¯ using cryogenic photoelectron-photofragment coincidence spectroscopy,” by Ben B. Shen, Yanice Benitez, Katharine G. Lunny, and Robert E. Continetti, Journal of Chemical Physics (2017). The article can be accessed at https://doi.org/10.1063/1.4986500 .
