Master of Science (M.Sc.)
Nathanael M Kidwell
John C Poutsma
Investigating and understanding the chemistry of the atmosphere has historically been an important research topic. This importance has only strengthened in the recent decades as technological advancements have drastically increased anthropogenic emissions of hydrocarbons and nitroaromatic compounds. Indeed, we are in an era of unprecedented change of the chemical composition of the troposphere and never before has an in-depth understanding of atmospheric chemical properties been more sought-after. This study seeks to fill that need by probing the molecular dynamics of atmospherically relevant molecules through the use of velocity map imaging (VMI). In particular, we utilize VMI to study the photolysis dynamics of brown carbon (BrC) chromophores and nitrosothiol compounds, as well as the collisional quenching dynamics of nitric oxide (NO) and molecular oxygen (O2). BrCs represent an important category of carbon-based aerosols that have, until recently, been considered spectroscopically similar to black carbon aerosols. It is now known that, due to nitroaromatic chromophores, BrCs absorb increasingly well from the visible region to the ultra-violet (UV) region. This study has shown that the probed nitroaromatic chromophores, nitrobenzene, ortho-nitrophenol, and nitroresorcinol, all yield nonstatistical energy partitioning. This deviation from statistical expectations is largely attributed to long-range dipole-dipole forces that inhibit the partitioning of energy to internal energy levels. Nitrosothiols are secondary aerosols that play a large role in the nucleation of aerosols as well as the formation of acid rain. Ion images of NO photofragments from 355 nm photolysis are largely anisotropic. The angular dependence of these images can be correlated to the dynamical signatures of dissociation process. Not only is NO and O2 collisional quenching a common occurrence in the atmosphere, it is also documented to take place during laser induced florescence experiments making data acquisition from such experiments difficult. Through the use of VMI combined with a dual channel pulse valve, the NO (X2Π) nonreactive collision product is probed. Analysis of state-resolved ion images indicates O2 (c1Σu-) is the preferred coproduct of this nonreactive collision. Additionally, product state distributions indicate a Λ-doublet propensity for NO (X2Π) rotational states. Physical properties, such as those determined in this study, are imperative for the formation of accurate climate models. Therefore, molecular dynamics studies are required to actively combat atmospheric hazards like air pollution and global climate change.
© The Author
Blackshaw, Kenneth Jacob, "Investigating the Molecular Choreography of Atmospherically Relevant Molecules: A Dynamics Study" (2019). Dissertations, Theses, and Masters Projects. Paper 1563899032.