Femtosecond Molecular Dynamics Studied with Vacuum Ultraviolet Pulse Pairs

摘要: Atoms and molecules have most of their oscillator strength in the vacuum ultraviolet (VUV)and extreme (XUV), between wavelengths 200 nm 30 nm. However,most femtosecond spectroscopy has been restricted to visible infrared due alack sufficiently intense VUV XUV light sources. This thesis discussesextensions pump/probe XUV, its application thedynamics ethylene oxygen excited at 161 nm.I begin with a detailed discussion short wavelength source used inthis work. The is based on high order harmonics near laser andcan deliver > 10 photons per shot pulses, corresponding nearly 10MW peak power XUV. Measurements harmonic yields as function thegeneration conditions reveal roles phase matching ionization gating highorder generation process.Pump/probe measurements are conducted using unique interferometer, capableof combining two different focus variable delay. ofVUV multiphoton allows for characterization interferometer.In molecules, time resolved fragment ion femtoseconddynamics system. range available pump probe be followed from photo-excitation all way dissociation without detectionwindow effects.The dynamics upon p r p* excitation protypical larger moleculesand thus served an important test case advanced ab initio molecular dynamicstheories. Femtosecond date, however, extremely lacking. Inthe present work, through series experiments pulses,time scales non-adiabatic relaxation electronic excitation, hydrogen migrationacross double bond, H2 molecule elimination measured compared theory.In simpler molecule, Schuman-Runge continuum leadsto direct along B 3 Su - potential energy curve. photoionspectra show that total photoionization cross section resembles twooxygen atoms within 50 fs after excitation.