.1 - Fluorine Naphthalene Clusters Of Resonant Two-photon Ionization And Ab Initio

Cluster is a transition state between the single molecule(atom) and condensation state,it represents the initial phase of condensation product.The hydrogen bond is one of the basic chemical forces,and effects the solvation,energy transfer,chemical reaction and so on.The weak or non-conventional hydrogen bond has been the subject of intense scrutiny over recent years. Compounds labelled with radioactive ¹⁸F may used in imaging techniques for the detection of cancers and some drug molecules are fluo-substituted,so the study of weak hydrogen bonding interactions involving F is surely expected to lead to new insights into the mode of binding and modes of action of these important compounds.While the hydrogen bond ctuster's structure analysis will guide us to understand the complex life phenomenon and mechenics from a simple level.Resonance enhanced two-photon(multi-photon) ionization(REMPI) technique Cooperated with time of fly spectroscopy can achieve dual selections(mass spectrum selection and spectroscopy selection) during the ionization and detection process.Compared with the other methods,the technique has much advancement:high sensitivity,elaborate selectivity,high resolution etc.Ever since then the method has been playing an important role in material composition analysis and so on.Meanwhile it has intersected with many fields and has got many returns.Aromatic molecular clusters combined via.van der Waals force or other weak bonds have been studied intensely both from the experimental and the theoretical points of view due to their importance in many physical and chemical phenomena.The study of structures,energies, and intramolecular dynamics of mass-resolved clusters of aromatic molecules by resonant two-photon ionization mass spectrometry(R2PI/MS) provides a powerful means to investigate such interactions.In this article,we combine the pulsed molecule beam,time of flight mass spectrum and the procedure of Gaussian O3 to research the two-photon ionization of 1-fluoronaphthalene(1FN) clusters.(1) The one-color resonant two-photon ionization(R2PI) spectrum of 1-fluoronaphthalene (1FN) dimer has been studied in the range from 304 nm to 322 nm by using supersonic molecular beam and time-of-flight mass spectrometer.Comparing with the original band O₀⁰(at 313.8nm) of S₁←S₀ transition of 1FN,a red-shifted band was observed in the 1FN dimer spectrum at about 315 nm with a relatively larger linewidth nearly 2 nm.Based on the consideration of inducing effect and ab initio calculations,this red-shifted band is assigned to the first electronic excited transition of 1FN dimer.A possible geometric structure of 1FN dimer is also obtained with calculations where the two 1FN molecules are combined through two hydrogen bonds which are composed between the hydrogen atom of a molecule and the fluorine atom of a neighboring molecule.The time-dependent(TD) calculation was also carried out and the result is consistent with the experiment.(2) Mass spectra of 1-fluoronaphthalene(1FN) cluster has been studied with UV laser ionization at 281nm by using supersonic molecular beam and time-of-flight mass spectrometer. (1FN)_n⁺(n=1-3) series cluster ions were obtained in the mass spectrum and its intensity decreases with cluster size n increasing.The laser intensity increasing induce an obvious peak position shift and split of the(1FN)⁺ in the mass spectrum,while it has little effect to the peak profiles of(1FN)₂⁺ and(1FN)₃⁺.The probable geometric structure of(1FN)₂ which is planar is obtained by using density functional theory(DFT) method at 6-311++g(d,p) basis set level.The ionization energy of(1FN)₂ is calculated to be 7.44eV which is little lower than the IP of mono-1FN(Experimental value is 8.15eV).So the 1FN clusters are probably ionized through two-photon process with such 281nm(4.41eV)UV laser.