Photoejection of molecules from the surface of a liquid microjet
thesisposted on 17.05.2010, 11:27 by Veronika Barinkova
A new instrument has been constructed for studying the dynamics of photochemical reactions at or near the surface of a liquid. In this apparatus, a liquid microjet is used to deliver a fresh and continuously flowing liquid surface into a high vacuum chamber. This system has been coupled with a laser pump-probe to produce and detect radicals. By using laser-induced fluorescence (LIF) spectroscopy, both the velocity distribution and the population of internal quantum states in the ejected molecules can be determined. Designing and building the apparatus required considerable attention with several significant adjustments being implemented to allow its operation. For instance, a series of traps were required to attain a vacuum in the low 10-5 mbar range. Using Fraunhofer diffraction the stability of the microjet has been demonstrated and the diameter has been confirmed to be 20 µm. To test the pump-probe procedure, a continuous microjet of a toluene/ethanol mixture has been subjected to laser photo-ejection using nanosecond pulses of 266 nm laser light. The time-of-flight distribution of toluene molecules ejected into the gas phase has been measured using time-resolved LIF spectroscopy. The velocity measurement indicated that the laser photejection process generated two groups of ejected molecules: (i) a collection of hyperthermal toluene molecules, which are assumed to be derived from molecules originally at or near the liquid surface and (ii) a group of slower, hotter molecules that most likely emanate from the liquid interior. Concise studies of the other liquid system namely aniline, benzene and acetyl acetone has also been made and are discussed in this thesis.