REMPI AND IMAGING STUDIES OF SINGLET O₂ FOLLOWING SPIN-FORBIDDEN PHOTODISSOCIATION OF OZONE

Aardema, Megan

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https://hdl.handle.net/2142/122401 Copy

Description

Title

REMPI AND IMAGING STUDIES OF SINGLET O₂ FOLLOWING SPIN-FORBIDDEN PHOTODISSOCIATION OF OZONE

Author(s)

Aardema, Megan

Contributor(s)

• North, Simon
• Meas, Benjamen
• Fast, Megan

Issue Date

2023-06-23

Keyword(s)

Photodissociation and photochemistry

Abstract

Ozone photodissociation in the Hartley (200-300 nm) and Huggins (310-370 nm) bands has been the focus of numerous studies due to its critical role in atmospheric chemistry. While Hartley band dissociation occurs primarily through two spin-allowed dissociation channels, three additional spin-forbidden channels have previously been observed following dissociation in the Huggins band. We report 1-D and 2-D REMPI spectra and velocity-mapped ion images of O₂(a¹∆g) and O₂(b¹Σ⁺) fragments following spin-forbidden dissociation in the Huggins band. We have previously observed a preference for the formation of even rotational states of O₂(a¹∆g) arising from Hartley band dissociation due to a Λ-doublet propensity. In the Huggins band, however, odd rotational states are enhanced in the REMPI spectrum, which we attribute to greater coupling between the initial excited state of O₃ and ³A′′ states producing odd rotational states of O₂(a¹∆g), than between the initial excited state and ³A′ states producing even rotational states. Ion image angular distributions of the O₂(a¹∆g) fragment in odd and even rotational states showed significant differences following Hartley band dissociation, supporting the Λ-doublet propensity model, but are indistinguishable following Huggins band dissociations. This supports a preference for the A′ Λ-doublet and even rotational states following O₃ transitions from the B state to ³A′ states and a preference for the A′′ Λ-doublet and odd rotational states following O₃ transitions from the B state to the ³A′′ states, but indicates that in the Huggins band, the A′′ Λ-doublet does not originate from a warmer distribution of parent molecules as seen in the Hartley band. 2D-REMPI allows simultaneous measurements of the rotational distributions for v=0-2 of the b¹Σ⁺ state as well as v=0 of the a¹∆g state. The relative signal in v=0-2 of the b¹Σ⁺ can provide information about the vibrational distribution, and rotational state distributions of each vibrational state can be fit individually. Spectra indicate a broad rotational distribution of the O₂(a¹∆g) fragment and a narrow distribution of the O₂(b¹Σ⁺) fragment. While determination of the O₂(a¹∆g) rotational distribution is limited due to the highly perturbed resonant state accessed in the REMPI scheme, a broad distribution is additionally supported by the multimodality of the radial distributions in the ion images.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

Handle URL

https://hdl.handle.net/2142/122401

DOI

https://doi.org/10.15278/isms.2023.6961

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