Guo-Jin Cao

Hydrogen bonds in the nucleobase-gold complexes: Photoelectron spectroscopy and density functional calculations

The nucleobase-gold complexes were studied with anion photoelectron spectroscopy and density functional calculations. The vertical detachment energies of uracil-Au(-), thymine-Au(-), cytosine-Au(-), adenine-Au(-), and guanine-Au(-) were estimated to be 3.37 ± 0.08 eV, 3.40 ± 0.08 eV, 3.23 ± 0.08 eV, 3.28 ± 0.08 eV, and 3.43 ± 0.08 eV, respectively, based on their photoelectron spectra. The combination of photoelectron spectroscopy experiments and density functional calculations reveals the presence of two or more isomers for these nucleobase-gold complexes. The major isomers detected in the experiments probably are formed by Au anion with the canonical tautomers of the nucleobases. The gold anion essentially interacts with the nucleobases through N-H···Au hydrogen bonds.

Interaction of ComO− (m = 1–3) with water: Anion photoelectron spectroscopy and density functional calculations

We investigated the reactions between cobalt-oxides and water molecules using photoelectron spectroscopy and density functional calculations. It has been confirmed by both experimental observation and theoretical calculations that dihydroxide anions, Co(m)(OH)(2)(-) (m = 1-3), were formed when Co(m)O(-) clusters interact with the first water molecule. Addition of more water molecules produced solvated dihydroxide anions, Co(m)(OH)(2)(H(2)O)(n)(-) (m = 1-3). Hydrated dihydroxide anions, Co(m)(OH)(2)(H(2)O)(n)(-), are more stable than their corresponding hydrated metal-oxide anions, Co(m)O(H(2)O)(n+1)(-).

Photodissociation and Density Functional Calculations of Small VmOn+ Clusters

Oxygen-poor vanadium oxide clusters, V2On+ (n = 1, 2), V3On+ (n = 1, 2, 3), and V4O3+, were produced by laser vaporization and were mass-selected and photodissociated with 532 and 266 nm photons. The geometric structures and possible dissociation channels of these clusters were determined based on the comparison of density functional calculations and photodissociation experiments. The experiments show that the dissociation of V2O+, V2O2+, and V3O3+ mainly occurs by loss of VO, while the dissociation of V3O+ and V4O3+ mainly occurs by loss of V atom. For the dissociation of V3O2+, the VO loss channel is slightly dominant compared to the V loss channel. The combination of experimental results and theoretical calculations suggests that the V loss channels of V3O+ and V4O3+ are single photon processes at both 532 and 266 nm. The VO loss channels of V2O2+ and V3O3+ are multiple-photon processes at both 532 and 266 nm.

Nonconventional Hydrogen Bonds between Silver Anion and Nucleobases: Size-Selected Anion Photoelectron Spectroscopy and Density Functional Calculations

We conducted combined gas-phase anion photoelectron spectroscopy and density functional theory studies on nucleobase-silver complexes. The most probable structures of the nucleobase-Ag- complexes were determined by comparing the theoretical calculations with the experimental measurements. The vertical detachment energies (VDEs) of uracil-Ag-, thymine-Ag-, cytosine-Ag-, and guanine-Ag- were estimated to be 2.18 ± 0.08, 2.11 ± 0.08, 2.04 ± 0.08, and 2.20 ± 0.08 eV, respectively, based on their photoelectron spectra. Adenine-Ag- has two isomers coexisting in the experiment; the experimental VDEs of the two isomers are 2.18 and 2.53 eV, respectively. In the most probable isomers of nucleobases-Ag-, uracil, thymine, and cytosine interact with Ag- anion via N-H···Ag and C-H···Ag hydrogen bonds, while adenine and guanine interact with Ag- anion through two N-H···Ag hydrogen bonds. The N-H···Ag hydrogen bonds can be characterized as medium or strong hydrogen bonds. It is found that binding sites of the Ag anion to the nucleobases are affected by the deprotonation energies and the steric effects of two adjacent X-H groups.

Structures and electronic properties of B2Si6−/0/+: anion photoelectron spectroscopy and theoretical calculations

We measured the photoelectron spectrum of B2Si6− anion and investigated the structures and electronic properties of B2Si6− anion as well as those of its neutral and cationic counterparts with quantum chemical calculations. The vertical detachment energy (VDE) of the B2Si6− anion has been measured to be 2.40 ± 0.08 eV. Through global minimum searches and CCSD(T) calculations, we have identified that the lowest-energy structures of B2Si6q (q = −1, 0, +1) are peculiar structures with a Si atom hanging over a distorted bowl-like B2Si5 framework. Quasi-planar or planar isomers have also been identified for the B2Si6 cluster at −1, 0, and +1 charge states. The quasi-planar and planar isomers are higher in energy than their bowl-like counterparts by at least 0.20 eV. The symmetries of the quasi-planar isomers varied at different charge states, ranging from Cs to C2h, then to D2h respectively for the −1, 0, and +1 charge states. The reducing of the symmetry from +1 charge state to −1 charge state is more likely due to the Jahn–Teller effect upon the addition of electrons.

Interaction of TiO2− with water: Photoelectron spectroscopy and density functional calculations

The interactions of titania with water molecules were studied via photoelectron spectroscopy and density functional calculations of TiO(OH)2(-) and Ti(OH)4(H2O)n(-) (n = 0-5) clusters which are corresponding to the TiO2(H2O)(-) and TiO2(H2O)n+2(-) (n = 0-5) systems, respectively. Experimental observation and theoretical calculations confirmed that TiO(OH)2(-) was produced when TiO2(-) interacts with one water molecule, and Ti(OH)4(H2O)n(-) (n = 0-5) were produced successively when TiO2(-) interacts with two or more water molecules. The structures of Ti(OH)4(H2O)n(-) with n = 4, 5 are slightly different from those of n = 1-3. The structures of Ti(OH)4(H2O)1-3(-) can be viewed as the water molecules interacting with the Ti(OH)4(-) core through hydrogen bonds; however, in Ti(OH)4(H2O)4,5(-), one of the water molecules interacts directly with the Ti atom via its oxygen atom instead of a hydrogen bond and distorted the Ti(OH)4(-) core.

The structural and electronic properties of NbSin−/0 (n = 3–12) clusters: anion photoelectron spectroscopy and ab initio calculations

Niobium-doped silicon clusters, NbSin- (n = 3-12), were generated by laser vaporization and investigated by anion photoelectron spectroscopy. The structures and electronic properties of NbSin- anions and their neutral counterparts were investigated with ab initio calculations and compared with the experimental results. It is found that the Nb atom in NbSin-/0 prefers to occupy the high coordination sites to form more Nb-Si bonds. The most stable structures of NbSi3-7-/0 are all exohedral structures with the Nb atom face-capping the Sin frameworks. At n = 8, both the anion and neutral adopt a boat-shaped structure and the openings of the boat-shaped structures remain unclosed in NbSi9-10-/0 clusters. The most stable structure of the NbSi11- anion is endohedral, while that of neutral NbSi11 is exohedral. The global minima of both the NbSi12- anion and neutral NbSi12 are D6h symmetric hexagonal prisms with the Nb atom at the center. The perfect D6h symmetric hexagonal prism of NbSi12- is electronically stable as it obeys the 18-electron rule and has a shell-closed electronic structure with a large HOMO-LUMO gap of 2.70 eV. The molecular orbital analysis of NbSi12- suggests that the delocalized Nb-Si12 ligand interactions may contribute to the stability of the D6h symmetric hexagonal prism. The AdNDP analysis shows that the delocalized 2c-2e Si-Si bonds and multicenter-2e NbSin bonds are important for the structural stability of the NbSi12- anion.