Date Thesis Awarded

5-2021

Access Type

Honors Thesis -- Access Restricted On-Campus Only

Degree Name

Bachelors of Science (BS)

Department

Chemistry

Advisor

Nathanael Kidwell

Committee Members

John Poutsma

Joshua Erlich

Andrew Petit

Abstract

Nitric oxide (NO) radicals are a common reactive intermediate and byproduct of incomplete combustion of fossil fuels, present in the atmosphere and interstellar medium. NO is also an important contributor to urban smog. Velocity map imaging was utilized to map the collisional quenching dynamics of NO (A2Σ+) with O2 to NO(X2Π, v′′=0,1 and O2 (X3Σg-). Evidence was found of O2 (c1Σu−) generated in coincidence with NO (X2Π) and a NO3 collision complex is formed prior to dissociation. Furthermore, the NO (X2Π, v′′=1, J′′, Fn, Λ) product state distributions reveal that NO is produced with a propensity to occupy the Π(A′′) Λ-doublet and thus with a preference to rotate perpendicular to the pπ∗ molecular orbital. Overall, the relative vibrational populations of NO resembled the Franck-Condon factors between the A2Σ+ and X2Π states of NO, indicating that the sudden or harpoon mechanism plays a pivotal role in the electronic quenching process.

Furthermore, using EOM-EA-CCSD//aug-cc-pVDZ, I investigated the probability that NO (A2Σ+) would be electronically quenched from its excited state via collisions with H2 and N2. For H2, we found that all interactions were repulsive with no quenching predicted. However, collisions with N2 showed that for NO in nitrogen-first orientations, NO underwent electronic quenching from angles of 90 to 135 degrees, with the lowest barrier to interaction at 111 degrees. The total spin density for N2 is inverted at the conical intersection (2.25 Å) to go from being localized around NO to N2. The charge distribution becomes more extreme, going from neutral at the asymptotic limit to a cationic NO (A2Σ+) and anionic N2, which enables the attraction that led to the conical intersection. The equations used to predict the electron transfer distance (from a harpoon mechanism) agree well with predictions of the conical intersection crossing distances.

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