Photoelectron Spectroscopy And Infrared Photodissociation Spectroscopy Of Nanoclusters In The Gas Phase

The potential applications of boron and its derivatives in the design of novel nanoclusters and materials are attracting increasing attention from researchers,and the transition metal oxides are utilized in catalysis and fuel cells.Combining gas phase spectroscopy with theoretical calculations,boron clusters have been observed and characterized in the past decades.Quasi-planar B36 cluster with a hexagonal vacancy and the first all-boron fullerenes D2d B40 and B40-were discovered.Subsequently,the concept of two-dimensional boron monolayer was proposed,which was named as borophene.Note the BO-and BO species are isovalent to CN-and CN/CO,respectively,the latter being well known inorganic ligands.This thesis reports on the gas phase spectroscopy and quantum chemical studies on boron-based clusters,metal-doped boron-oxygen clusters and metal oxides carbonyl complexes.Specifically,boron sulfide clusters,metal-doped boron oxide clusters,and tantalum oxide carbonyl complexes in the gas phase were prepared using the laser vaporization supersonic molecular beam techniques.Combining theoretical calculations and photoelectron spectroscopy or infrared photodissociation spectroscopy,we characterize their global minimum structures and elucidate their electronic properties and chemical bonding.The main results are as follows:1.Cationic B4O4+ cluster:double(? and ?)aromaticityHere we report the structural,electronic,and bonding properties of the B4O4+cationic cluster on the basis of unbiased Coalescence Kick global-minimum searches and first-principles electronic structural calculations at the B3LYP and single-point CCSD(T)levels.The B4O4+cluster is proven to possess a Cs global minimum structure It represents the smallest boron oxide species with a hexagonal boroxol(B3O3)ring as the core,terminated by a boronyl group.Chemical bonding analyses reveal double(?and ?)aromaticity in Cs B4O4+,which closely mimics that in the 3,5-dehydrophenyl cation C6H3+(D3h,1A1'),a prototypical molecule with double aromaticity.Alternative D2h(2B3g)and C2v(2A1)isomeric structures of B4O4+are also analyzed,which are relevant to the global minima of B4O4 neutral and B4O4-anion,respectively.These three structural motifs vary drastically in terms of energetics upon changing the charge state.This system also demonstrates a crucial idea in nanoclusters that each electron in the valence shell is important.2.Binary B2Sn-/0(n=2-7)clustersCombined photoelectron spectroscopy and the density functional theory(DFT)we establish the global minimum(GM)structures of the B2Sn-/0(n=2-7)species.As the S atom increases,a heteroatomic closed ring in B2Sn-(n=2-7)anion species gradually forms triangular B2S ring,rhombic B2S2 ring and pentagonal B2S3 ring.As for the B2Sn(n=2-7)neutral species,the GM structures are composed of a BS2 linear chain and a BSn(n=2-4)closed ring.Bonding analysis shows that there are a variety of forms of delocalized ? bonds in the clusters.Besides,the electron affinities of neutral counterparts of the B2Sn-(n=4-7)species increase with the number of S atoms,suggesting the formation of superhalogens.3.Competitive oxidation of B versus Al centers in ternary Al-B-O clustersWe report a combined photoelectron spectroscopy and density-functional study on the structural,electronic,and bonding properties of AlnBO2-and AlnBO2(n=2,3)clusters.Coalescence-kick global searches allow the identification of their candidate structures.The GM structures are confirmed via comparisons with experiments.The BO2 block(linear O=B=O chain)is nonexistent in any of the anion and neutral species,which is remarkably different from the M(BO2)n(M=Cu,Au,Mn,Fe)complex clusters in the literature.The Al2BO2-anion is V-shaped in geometry,Cs(1A'),with an Al center connecting to OB and OAl terminals.Al3BO2-has a Cs(2A")global minimum,in which an Al2 dimer interacts with bridging boronyl(BO)and an OAl unit.Its low-lying C2v(2B2)isomer consists of boronyl and OAl that are doubly bridged by two Al atoms.Chemical bonding analysis in these Al-B-O clusters shows that the cluster structures are support the concept of sequential and competitive oxidation of B versus Al centers in AlnB.The first 0 atom prefers to oxidize B and form BO,whereas the second 0 atom has options to interact with a fresh Al/Aln/AlnB unit or a BO group.These ternary clusters are molecular models for the oxidation or combustion of the B/Al system,a typical high energy density material.4.Tantalum oxide carbonyl complexWe have produced the tantalum oxide carbonyl complex cations TaO(CO)n+(n=3-8)in the gas phase.The experimental data confirm that the infrared bands(2065-2110 cm-1)of TaO(CO)n+(n=3-8)are much lower than the frequency of free CO molecule(2143 cm-1),indicating strong ? back-donation interactions.The five-coordinate carbonyl complexes TaO(CO)5+are fully coordinated with 18 valence electrons Chemical bonding analysis reveal that four-coordinate carbonyl complex TaO(CO)4+possesses 10-electron planar configuration.The TaO(CO)n+ cation species are typical transition metal carbonyl complexes.