High resolution infrared spectra of a carbon dioxide molecule solvated with helium atoms

Infrared spectra of He(N)-CO(2) clusters with N up to about 20 have been studied in the region of the CO(2) nu(3) fundamental band ( approximately 2350 cm(-1)) using a tunable diode laser spectrometer and pulsed supersonic jet source with cooled (>-150 degrees C) pinhole or slit nozzles and high backing pressures (<40 atm). Compared to previous studies of He(N)-OCS and -N(2)O clusters, the higher symmetry of CO(2) results in simpler spectra but less information content. Discrete rotation-vibration transitions have been assigned for N=3-17, and their analysis yields the variation of the vibrational band origin and B rotational constant over this size range. The band origin variation is similar to He(N)-OCS, with an initial blueshift up to N=5, followed by a monotonic redshift, consistent with a model where the first five He atoms fill a ring around the equator of the molecule, forcing subsequent He atom density to locate closer to the ends. The B value initially drops as expected for a normal molecule, reaching a minimum for N=5. Its subsequent rise for N=6 to 11 can be interpreted as the transition from a normal (though floppy) molecule to a quantum solvation regime, where the CO(2) molecule starts to rotate separately from the He atoms. For N>13, the B value becomes approximately constant with a value about 17% larger than that measured in much larger helium nanodroplets.     

Infrared-infrared double resonance spectroscopy of cyanoacetylene in helium nanodroplets

Infrared-infrared double resonance spectroscopy is used as a probe of the vibrational dynamics of cyanoacetylene in helium droplets. The nu1 C-H stretching vibration of cyanoacetylene is excited by an infrared laser and subsequent vibrational relaxation results in the evaporation of approximately 660 helium atoms from the droplet. A second probe laser is then used to excite the same C-H stretching vibration downstream of the pump, corresponding to a time delay of approximately 175 micros. The hole burned by the pump laser is narrower than the single resonance spectrum, owing to the fact that the latter is inhomogeneously broadened by the droplet size distribution. The line width of the hole is characteristic of another broadening source that depends strongly on droplet size.     

The interaction of metastable helium atoms with alkali atoms

Using crossed beams of ground state alkali atoms A (A = Li, Na, K, Rb, Cs) and metastable He(2³ S), He(2¹ S) atoms, we have measured the energy spectra of electrons resulting in the respective Penning ionization processes at: thermal collision energies. The data are interpreted to yield the well depthD _e ^* of the²Σ interaction potentials as follows: He(2³ S)+A:D _e ^* (A=Li)=868(20) meV;D _e ^* (Na)=740(25) meV;D _e ^* (K)=591(24) meV;D _e ^* (Rb)=546(18) meV;D _e ^* (Cs)=533(18) meV. He(2¹ S)+A:D _e ^* (Li)=330(17) meV;D _e ^* (Na)=277(24) meV;D _e ^* (K)=202(23) meV;D _e ^* (Rb)=219(18) meV;D _e ^* (Cs)=277(18) meV. The well depth for He(2³ S)+A(²Σ) is always close to 80% of the well depth for Li(2s)+A(X ¹Σ). The ionization cross sections for He(2¹ S)+A are about 3 to 4 times larger than those for He(2³ S)+A.     

Reaction of hydrogen atoms with hydroxide ions to give solvated electrons

Exposure of aqueous alkaline glasses to ⁶⁰Co γ-rays followed by photobleaching to remove e_t⁻ resulted in E.S.R. spectra dominated by O_t^- and H·_t^-, but at ca. 110 K H·_t was lost and e_t⁻ reappeared.     

Rotational spectrum of BiBr

The microwave absorption spectra of Bi⁷⁹Br and Bi⁸¹Br have been measured in the 65–100 GHz region. Frequencies of rotational transitions (υ,J + 1) ← (υ,J) in the 0⁺ electronic ground state with J = 26,27 and 35–39, and in the vibrational state υ = 0–11 can be fitted to the expression: ν = 2[Y₀₁ + Y₁₁(υ + $\text{1}\text{2}$) + Y₂₁(υ + $\text{1}\text{2}$)²] (J + 1) + 4Y₀₂(J + 1)³. The results for the Dunham coefficients are: Y₀₁ = 1295.5609(12) MHz, Y₁₁ = ?3.97809(18) MHz, Y₂₁ = 2.303(18) kHz, Y₀₂ = ?220.26(45) Hz for Bi⁷⁹Br, and: Y₀₁ = 1272.3406(12) MHz, Y₁₁ = ?3.87164(16) MHz, Y₂₁ = 2.225(14) kHz, Y₀₂ = ?212.31(45) Hz for Bi⁸¹Br. From these results we have deduced the value for the equilibrium distance r_e, for the potential constants a₀ and a₁, and for the vibrational constants ω_e and ω_eχ_e. The molecular constants of BiBr are almost the same as of TIBr, the situation found also for BiI and TII.     

Dispersion interaction between helium atoms

Accurate values for the coefficients of the R^?6, R^?8 and R^?10 in the series representation of the dispersion interaction between two helium atoms at distance R are obtained by a simple variation method.     

Photoionization of helium nanodroplets doped with rare gas atoms

Photoionization of He droplets doped with rare gas atoms (Rg=Ne, Ar, Kr, and Xe) was studied by time-of-flight mass spectrometry, utilizing synchrotron radiation from the Advanced Light Source from 10 to 30 eV. High resolution mass spectra were obtained at selected photon energies, and photoion yield curves were measured for several ion masses (or ranges of ion masses) over a wide range of photon energies. Only indirect ionization of the dopant rare gas atoms was observed, either by excitation or charge transfer from the surrounding He atoms. Significant dopant ionization from excitation transfer was seen at 21.6 eV, the maximum of He 2p 1P absorption band for He droplets, and from charge transfer above 23 eV, the threshold for ionization of pure He droplets. No Ne+ or Ar+ signal from droplet photoionization was observed, but peaks from HenNe+ and HenAr+ were seen that clearly originated from droplets. For droplets doped with Rg=Kr or Xe, both Rg+ and HenRg+ ions were observed. For all rare gases, Rg2+ and HenRgm+ (n,m> or =1) were produced by droplet photoionization. Mechanisms of dopant ionization and subsequent dynamics are discussed.     

Germanium nanoparticles from solvated atoms: synthesis and characterization

Germanium nanoparticles were synthesized by the chemical liquid deposition method (CLD) in which the Ge atoms, produced resistively, were co-deposited with 2-propanol, acetone and tetrahydrofurane vapors to obtain colloidal dispersions. The colloidal dispersions were characterized by UV-vis spectrophotometry, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and Infrared Spectroscopy (FTIR) techniques. The Germanium colloids are, in general, kinetically unstable. Strong absorption bands in the UV region suggest that nanoparticles obtained by this procedure exhibit quantum confinement. In the Ge colloids, the particle size distribution is highly sensitive to concentration change. For example, the TEM measurements revealed for the Ge-2-propanol colloid, particle sizes close to 3 nm for a concentration of 10^–3 M and 30 nm for a concentration of 10^–2 M. The HRTEM and SAED showed the high crystallinity of the nanoparticles, and it was possible to observe the typical lattice spaces of a diamond cubic Ge structure. The FTIR studies revealed the Ge-organic nature of the particles surface. Mechanisms and structures have been proposed for surface reactions.     

Rotational spectrum of cis-cis HOONO

The pure rotational spectrum of cis-cis peroxynitrous acid, HOONO, has been observed. Over 220 transitions, sampling states up to J'=67 and Ka'=31, have been fitted with an rms uncertainty of 48.4 kHz. The experimentally determined rotational constants agree well with ab initio values for the cis-cis conformer, a five-membered ring formed by intramolecular hydrogen bonding. The small, positive inertial defect Delta=0.075667(60) amu A2 and lack of any observable torsional splittings in the spectrum indicate that cis-cis HOONO exists in a well-defined planar structure at room temperature.     

Photoelectron imaging of helium droplets doped with Xe and Kr atoms

Helium droplets doped with Xe and Kr atoms were photoionized by using VUV synchrotron radiation from the Advanced Light Source and the resulting photoelectron images were measured. A wide range of He droplet sizes, photon energies, and dopant pick-up conditions was investigated. Significant ionization of dopants was observed at 21.6 eV, the absorption maximum of 2p (1)P1 electronic excited state of He droplets, indicating an indirect ionization mechanism via excitation transfer. The photoelectron images and spectra reveal multiple photoionization mechanisms and pathways for the photoelectrons to escape the droplet. Specifically, they show sets of sharp peaks assigned to two mechanisms for Penning ionization of the dopant by He* in which the photoelectrons leave the droplet with no detectable energy loss, a broad, intense feature representing electrons that undergo significant energy loss, and a small amount of ultraslow electrons that may result from electron trapping at the droplet surface. The droplet-size dependence of the broad, intense feature suggests the development of the conduction band edge in the largest droplets seen here ((N) approximately 250,000).     

Rotational and vibrational dynamics of ethylene in helium nanodroplets

Rotationally resolved infrared spectra are reported for the asymmetric C-H stretching fundamental bands of C(2)H(4) in helium nanodroplets, as well as two weak combination bands. The J=2 rotor levels are strongly shifted from the energies estimated from a rigid rotor calculation and can be accounted for with two centrifugal distortion constants. The excited states of the three bands with B(3u) symmetry are strongly coupled in the gas phase and exhibit lifetimes >100 ps in helium, with the upper member of the polyad exhibiting the shortest lifetime. In contrast, the nu(9) band (B(2u) symmetry) exhibits very broad, homogeneously broadened line profiles (full width at half maximum approximately 0.5 cm(-1)) corresponding to an excited state lifetime of approximately 10 ps. This short lifetime is presumed to be due to an efficient, solvent mediated vibration-to-vibration relaxation process. In addition, the absence of transitions to the 2(21) and 2(20) rotor levels in the nu(9) band suggests they form rotational resonances with the elementary modes of helium, resulting in very short excited state lifetimes of less than 2 ps.     

Laser-assisted electron-impact excitation of hydrogen and helium atoms

The excitation of H(1s–2s) and He(1¹ S–2¹ S) by electron impact in the presence of a nonresonant laser field is studied in the framework of the perturbation theory. The wavelength variation of the total cross section is presented at incident electron energies of 100 eV and 200 eV for hydrogen and 200 eV for helium. The use of pseudostates as intermediate states in the study of excitation of hydrogen is also investigated.     

The vibrational relaxation of ozone by helium atoms

An ab initio, quantum-mechanical method is used to compute rate coefficients for the vibrational relaxation of ozone in three-dimensional collisions with helium atoms. Good agreement is obtained between the calculated and experimental rate coefficients for the process He + O₃(010) ? He + O₃(000).     

Hydrosilylation of 1-hexyne promoted by acetone solvated gold atoms derived catalysts

Supported gold nanoparticles, prepared by deposition of acetone solvated Au atoms on supports as carbon and γ-Al₂O₃, behave as valuable catalysts for the regioselective hydrosilylation of 1-hexyne with different silanes. The catalytic behaviour of gold-based systems is compared with the activity of supported platinum catalysts and a different affinity between the metals and the silanes is observed.     

Radial correlation limits of helium and heliumlike atoms

Radial correlation limits of two-electron atoms with atomic numbers Z = 1–10 are calculated by using modified Kinoshita wave functions in which all the parameters are optimized. The optimal Kinoshita functions show a rapid energy convergence with the increasing number N of constituent terms, and the radial energies convergent to 10 significant figures are obtained. The results show that both the calculated and estimated values of the radial correlation limits in the literature are insufficiently accurate. In the case of He, for example, the present calculation gives ?2.879 028 764 hartrees with N = 40, while the best literature value is ?2.879 028 6 hartrees.     

Insertion of noble gas atoms into cyanoacetylene: an ab initio and matrix isolation study

A computational and experimental matrix isolation study of insertion of noble gas atoms into cyanoacetylene (HCCCN) is presented. Twelve novel noble gas insertion compounds are found to be kinetically stable at the MP2 level of theory, including four molecules with argon. The first group of the computationally studied molecules belongs to noble gas hydrides (HNgCCCN and HNgCCNC), and we found their stability for Ng = Ar, Kr, and Xe. The HNgCCCN compounds with Kr and Xe have similar stability to that of previously reported HKrCN and HXeCN. The HArCCCN molecule seems to have a weaker H-Ar bond than in the previously identified HArF molecule. The HNgCCNC molecules are less stable than the HNgCCCN isomers for all noble gas atoms. The second group of the computational insertion compounds, HCCNgCN and HCCNgNC, are of a different type, and they also are kinetically stable for Ng = Ar, Kr, and Xe. Our photolysis and annealing experiments with low-temperature cyanoacetylene/Ng (Ng = Ar, Kr, and Xe) matrixes evidence the formation of two noble gas hydrides for Ng = Kr and Xe, with the strongest IR absorption bands at 1492.1 and 1624.5 cm(-1), and two additional absorption modes for each species are found. The computational spectra of HKrCCCN and HXeCCCN fit most closely the experimental data, which is the basis for our assignment. The obtained species absorb at quite similar frequencies as the known HKrCN and HXeCN molecules, which is in agreement with the theoretical predictions. No strong candidates for an Ar compound are observed in the IR absorption spectra. As an important side product of this work, the data obtained in long-term decay of KrHKr+ cations suggest a tentative assignment for the CCCN radical.     

Rotational spectrum and internal dynamics of tetrahydrofuran-krypton

The rotational spectrum of the tetrahydrofuran-krypton van der Waals complex has been investigated by pulsed-jet Fourier transform microwave spectroscopy. The spectra of the (84)Kr and (86)Kr isotopologues have been assigned and the krypton atom is located nearly over the oxygen atom, almost perpendicular to the COC plane. Each rotational transition is split into two component lines due to, according to the observed Coriolis coupling term between the tunneling states, the residual pseudorotational effects of the ring in the complex. The splitting between the two vibrational sublevels is 87.462(2) and 87.062(2) MHz for the (84)Kr and (86)Kr isotopologues, respectively. These splittings have been used to determine the barrier to inversion, B(2) = 67 cm(-1). The dissociation energy has been estimated to be 3.7 kJ mol(-1) from centrifugal distortion effects.     

Excited state dynamics of Ag atoms in helium nanodroplets

The excited state dynamics of silver atoms embedded in helium nanodroplets have been investigated by a variety of spectroscopic techniques. The experiments reveal that 5p 2P1/2 <-- 5s 2S1/2 excitation of embedded silver atoms results almost exclusively in the ejection of silver atoms populating the 2P1/2 state. In contrast, excitation to the 5p 2P3/2 state leads to the ejection of not only silver atoms in the 2P1/2, 2P3/2, and 2D5/2 excited states but also of AgHe and AgHe2. These AgHe exciplexes are mainly formed in the A2Pi1/2 electronic state. In addition, it is found that a considerable fraction of the 2P3/2 excited silver atoms become solvated within the helium droplets, most probably as AgHe2. The observations can be accounted for by a model in which the metastable 2D5/2 state of silver acts as a doorway state in the relaxation of 2P3/2 excited silver atoms.