Photodissociation Dynamics Of Vacuum Ultraviolet Of Gas Phase Water Molecules And Carbon Dioxide

This thesis includes two parts:Photodissociation dynamics of vacuum ultraviolet of gas phase water molecules and carbon dioxide.Part?:Investigations of the photofragmentation patterns of both light and heavy water at the state-to-state level are a pre-requisite for any thorough understanding of chemical processing and isotope heterogeneity in the interstellar medium?ISM?.Here we reveal dynamical features of the dissociation of water molecules following excitation to the??010?state using a tunable vacuum ultraviolet source in combination with the high resolution H?D?-atom Rydberg tagging time-of-flight technique.The action spectra for forming H?D?atoms and the OH?OD?product state distributions resulting from excitation to the??010?states of H₂O and D₂O both show striking differences,which are attributable to the effects of an isotopologue-specific accidental resonance.Such accidental resonance induced state mixing may contribute to the D/H isotope heterogeneity in the Solar System.The present study provides an excellent example of competitive state-to-state non-adiabatic decay pathways involving at least five electronic states.Part?:State-to-state photodissociation of carbon dioxide?CO₂?via the 3p¹?_u Rydberg state was investigated by the time-sliced velocity map ion imaging technique?TSVMI?with the tunable vacuum ultraviolet free electron laser?VUV FEL?source.Raw images of the O?¹S?products resulting from O?¹S?+CO?X¹?⁺?channel were acquired at the photolysis wavelengths between 107.37 and 108.84 nm.From the vibrational resolved O?¹S?images,the product total kinetic energy releases and the vibrational state distributions of the CO?X¹?⁺?co-products were obtained.It is found that vibrationally excited CO co-products populate as high as v=6 or 7 with peaking at v=1 and v=4,and most of individual vibrational peaks present a bimodal rotational structure.Furthermore,the vibrational-state specific anisotropy parameter?at all studied photolysis wavelengths has also been determined.The?-values exhibit a photolysis wavelength dependent feature,in which more positive?-values are observed at 108.01 nm and 108.27 nm than those at 107.37 nm and 107.52 nm,While at108.84 nm,the?-values behave a little isotropic.These experimental results indicate that the VUV excited CO₂ molecule around 108 nm should non-adiabatic transit to the 4¹A?state followed by dissociation on the 4¹A?state to produce O?¹S?+CO?X¹?⁺?products with different dissociation time scale.