Experimental And Theoretical Investigations On Molecular Structures Of Several Gaseous Ionic Clusters

Mass spectrometry combined with spectroscopy analysis is a powerful approach to analyze molecular structures and properties of gas phase ionic clusters.With the aid of quantum chemistry calculations,the spectra of the mass-selected ionic clusters can be assigned,deducing the geometric and electronic structures,intramolecular bonding,as well as the intermolecular interactions.In this thesis,the infrared photodissociation spectroscopy and negative ion photoelectron spectroscopy have been applied on the sequential and synergistic CO-release processes of the carbonyl iron complexes,and the interactions between hexafluoroisopropanol(HFIP)molecules and halides.(1)Orientation-specific charge-dipole interactions between hexafluoroisopropanol and halides:HFIP is a common solvent for polymerization reactions due to its strong hydrogen-bond donating ablity.Thus,it is also an ideal object in gas phase to model the intermolecular interactions in condensed phase.The gaseous complex[HFIP·X]-(X=F,Cl,Br,and I)have been studied with the negative ion photoelectron spectroscopy(NIPES)coupled with an electronspray ion source,as well as theoretical calculations.The spectral analysis shows that a neutral HF molecule is formed upon HFIP interacting with F-via proton transfer,rendering a stable structure of[HFIP-H-·HF],while the other halides maintain the structure of[HFIP·X]-(X=Cl,Br,and I).Moreover,the HFIP moiety prefers the synperiplanar(SP)configuration among all[HFIP·X]-(X=F,Cl,Br,and I)isomers,although the antiperiplanar(AP)conformer is suggested to be the most stable for the neutral HFIP monomer,while the SP structure is unstable.The calculated binding energies of[HFIP·X]-(X=F,Cl,Br,and I)in the AP and SP configurations,confirm that the significant geometry change is attributed to the orientation-specific charge-dipole interactions between HFIP and halides.(2)Infrared photodissociation spectroscopy combined with time-of-flight mass spectrometry:The spectroscopy of gas phase transition-metal compounds can provide useful information to reveal the correlation between their molecular structures and catalytic performance at microscale.For this purpose,we have contructed an equipment of infrared photodissociation spectroscopy combined with time-of-flight mass spectrometer.It consists of a laser ablation ion source,a two-level tandem time-of-flight mass spectrometer,an ion trap,and an OPO/OPA IR laser system.The Fe and Au samples have been used to test its performance by recording the photodissociation spectra of mass-selected metal clusters,verifying the reliability of the ion source to produce a variety of metal carbonyl ion complexes.A mass resolution(M/?M)is over 1300,and a tunable IR range covers from 700 to 4000 cm-1 with a typical spectral resolution of 1.8 cm-1,both of which can satisfy the experimental requirements for most future researches.Specially,a novel electric controlling method is designed for the ion trap,which can efficiently make the deceleration and storage of target ions with high kinetic energy from the time-of-flight mass analyser.(3)CO-release mechanism in infrared photodissociation of Fe3(CO)12+:Dodecarbonyl triiron,is not only as a common industrial catalyst,but also a potential CO-releasing materials(CORMs)for medical treatments.Using the home-made infrared photodissociation spectroscopy coupled with a time-of-flight mass spectrometer,we have performed a IR photodissociation study of Fe3(CO)12+.With the aid of high accuracy quantum chemical calculations,the most stable Fe3(CO)12+configuration is found to be an open chain one like[Fe(CO)5-Fe(CO)2-Fe(CO)5]+,where the chemical bonds between the CO ligand with the Fe+ cation contain the high ionic bonding characters.As the middle Fe-CO bond is weaker than those in both ends Fe(CO)5+ building block,the middle Fe-CO bond is preferred to be broken up after photoexcitation by an infrared photon.Moreover,by comparing the experimental and calculated spectra of all fragment ions,we can draw a conclusion of the CO-release mechanism in IR photodissociation of Fe3(CO)12+,which contains the competeing processes of the sequential and synergistic dissociations.