This thesis describes laboratory experiments and electronic structure calculations on three chemical systems relevant to tropospheric ozone chemistry: peroxynitrous acid (HOONO), hydroxymethylperoxy radical formed from HO2 + HCHO (R1), and products of alkoxy isomerization (R2). R1 and R2 were studied experimentally using a gas flow cell that combined UV photolysis with cavity ringdown spectroscopy (CRDS). All chemical systems were studied using electronic structure calculations and kinetics modeling. HOONO is one of the products of the...