This dissertation presents a study of photoionization dynamics of doped helium nanodroplets. It is motivated by a desire to gain better insight into the interactions between charged particles and finite-sized He droplets.

From VUV single photon ionization on He nanodroplets doped with rare gases, ion product mass distributions and photoion yields have been obtained via high-resolution time-of-flight mass spectrometry, which suggests that when He droplets are subject to absorption, indirect Penning ionization dominates the ion formation mechanism. The kinetic energy and angular distribution of ejected photoelectrons acquired by photoelectron imaging further unravel detailed excitation, ionization and post-ionization dynamics resulting from initial excitation of doped He droplets to the 2 ¹P ₁ electronic excited state.

From UV-based resonant enhanced multi-photon ionization of aniline and indole embedded in pulsed He droplets, the direct ionization has been examined. The resulting electron spectra are featured with faster electrons and asymmetric broadening to the lower kinetic energy side. The former effect has been attributed to lowering of the ionization threshold caused by stabilization of the ionic dopant in the He droplet, whereas the latter can be understood by the electron relaxation in the droplet. Moreover, features with different polar properties tend to exhibit different response to the polarizable He droplets environment. Photoelectron imaging of He droplets generated from a pulsed droplet source has been demonstrated for the first time. The photoelectron spectrum of doped He droplets generated from a pulsed droplet source exhibits similar properties with that of doped He droplets generated from a continuous droplet source, except a stronger solvent effect is observed as a result of a larger average droplet size.

Complex photoionization dynamics have been revealed in doped He droplets. Nevertheless, it is found that He droplets play a critical role in determining the ion formation process in doped He droplets, as well as the final electron energy and angular distributions. These observations point to substantial interactions between charged particles and the finite-sized He droplets environment upon ionization.