Resonance enhanced three-photon absorption of molecular iodine

D ← X resonance enhanced three-photon excitation spectrum of iodine was observed by a cw intracavity absorption technique. Vibrational quantum numbers of D ← X transitions are given for every major spectral feature. The corresponding one-photon enhancement from the B state is evident from the one-photon vibrational assignment. The spectroscopic constants for the D state are v₀₀ = 40 998 cm^?1 ω′₀ = 113 cm^?1 and ω′₀χ′₀ = 0.045 cm^?.     

Surface enhanced Raman spectra of nucleic acid components adsorbed at a silver electrode

High-resolution vibrational spectra of nucleic acid components adsorbed on a silver electrode were obtained using a spectroelectrochemical method based on the large-intensity enhancement for Raman scattering at electrode surfaces.The laser surface Raman spectra of purine, adenine, adenosine, deoxyadenosine, adenine mononucleotides, adenylyl-3′, 5′-adenosine and polyriboadenylic acid were recorded in the range of 150–3500 cm^?1. The intensities of the vibrational bands were highly dependent upon the electrochemical preparation of the electrode, the applied potential and the nature of the adsorbate species. High-intensity spectra in rather dilute bulk solutions were obtained.The phosphate derivatives of adenosine exhibited strongly enhanced Raman scattering. Spectral band frequencies corresponded closely with normal Raman spectra of these molecules in solution. The adenine ring breathing mode at 740 cm^?1 and the adenine ring skeletal vibration at 1335 cm^?1 produced prominent Raman scattering. A strong band at about 240 cm^?1 for the adenine mononucleotides was attributed to silver/adsorbed phosphate group vibrations.     

Near infrared electronic spectrum of TCNQ mono-valent anion

The high resolution near infrared electronic spectrum of TCNQ anion dissolved in 2-methyltetrahydrofuran glass at 77 K has been determined. The absorption bands are interpreted as simple progressions of two molecular vibrations in a single electronic excited state with ν₀₀ = 11661 cm^?1. The molecular vibrations (ω′₁ = 1264 ± 3 cm^?1, ω′₂ = 335 ± 3 cm^?1) of the vibrational progression agree well with observed Raman active transitions. The experimental data do not require the presence of two electronic transitions in the 1.3 to 2.1 eV region, contrary to what had been assumed previously on the basis of less well resolved room temperature spectra.     

Two-photon absorption spectrum of (2,2)-paracyclophane

The two-photon absorption spectrum of crystalline (2,2)-paracyclophane was measured in the regions of 31200–33800 cm^?1, 34700–36500 cm^?1, and 40800–48600 cm^?1 by monitoring the fluorescence intensity using a tunable dye laser as a two-photon excitation source. Two absorption bands in the region 34700–36500 cm^?1 were assigned to the two even-parity allowed ¹B_1g ← ¹A_1g and ¹B_2g ← ¹A_1g transitions.     

An ab initio calculation of symmetric bending and stretching vibrational states of the H3O+ and D3O+ ions

Calculations are reported for the symmetric bending and stretching vibrational states of H₃O⁺ and D₃O⁺ including coupling between these two modes. The calculations were carried out by using a potential surface calculated by the SCF CI method and expressed in terms of symmetric internal coordinates. The transition energy of the ν₂ (1^? ← 0⁺) inversion mode is found to be 985 cm^?1, which is comparable to the experimental value of 954.417 cm^?1 observed by Haese and Oka. The calculated inversion doubling of the lowest state is 51 cm^?1.     

On spectroscopic properties and isotope effects of vibrationally stabilized molecules

Results of quantum and semiclassical calculations obtained for two different potential-energy surfaces are used to discuss spectroscopic properties and isotope effects of the linear IHI and IDI molecules. The potentials are a purely repulsive LEPS surface and a DIM-3C potential with two van der Waals type minima for equivalent IH ··· I and I ··· HI configurations. Both systems are dominated by the effect of vibrational bonding giving rise to some very unusual spectroscopic phenomena, which are discussed in detail. The different vibrational frequencies and rotational constants are roughly estimated as ν₁ = 120 (100) cm^?1, ν₂ = 280 (210) cm^?1, ν₃ = 360 (160) cm^?1 and B = 0.0194 (0.0196) cm^?1 for IHI (IDI). A detailed discussion of the dependence of ν₁, ν₂ and B on ν₃, their sensitivity to variations of the potential-energy surface, and a comparison with the vibrational frequencies of I₂ and HI (ID) is given. It is predicted that there exists only one excited level of the antisymmetric stretching mode. The numbers of symmetrical stretching and bending levels are fairly constant or may even decrease upon deuteration. Simultaneously deuteration destabilizes the molecule. These unusual phenomena are rationalized by our calculations. A set of criteria for observing infrared and Raman bound-to-bound and bound-to-resonance state transitions are presented for the IHI and IDI molecule.     

Excited states of the polyacetylenes. Analysis of the near ultraviolet spectra of diacetylene and triacetylene

The 2000–2800 Å system of diacetylene and the 2300–3000 Å system of triacetylene have been investigated. Analysis of the vibrational structure indicates that we observe transitions to a ¹Δ_u upper electronic state for both molecules and transitions to a ¹Σ^?_u state for diacetylene.     

Surface Charges at the CaF2/Water Interface Allow Very Fast Intermolecular Vibrational‐Energy Transfer

We investigate the dynamics of water in contact with solid calcium fluoride, where at low pH, localized charges can develop upon fluorite dissolution. We use 2D surface‐specific vibrational spectroscopy to quantify the heterogeneity of the interfacial water (D₂O) molecules and provide information about the sub‐picosecond vibrational‐energy‐relaxation dynamics at the buried solid/liquid interface. We find that strongly H‐bonded OD groups, with a vibrational frequency below 2500 cm^?1, display very rapid spectral diffusion and vibrational relaxation; for weakly H‐bonded OD groups, above 2500 cm^?1, the dynamics slows down substantially. Atomistic simulations based on electronic‐structure theory reveal the molecular origin of energy transport through the local H‐bond network. We conclude that strongly oriented H‐bonded water molecules in the adsorbed layer, whose orientation is pinned by the localized charge defects, can exchange vibrational energy very rapidly due to the strong collective dipole, compensating for a partially missing solvation shell.     

Rotational tunnelling of methane on the surface of graphitized carbon blacks studied by neutron scattering spectroscopy

Rotational tunnelling transitions of methane adsorbed on the surface of graphitized carbon black have been observed by incoherent neutron inelastic scattering. Two transitions have been observed, at 58 μeV and 108 μeV, which arise from the barrier to rotation about axes parallel to the surface. The methane molecules undergo rotational diffusion about an axis perpendicular to the surface. The tunnelling transitions are quite sharp at 6 K but become broader as the temperature is raised. At 30 K the motion is best described as isotropic rotational diffusion. The tunnelling spectrum has been observed on two different graphitized carbon blacks, Vulcan III (71 m² g^?1) and Sterling FT (11 m² g^?1). the latter has a more homogeneous surface and gives a sharper spectrum. Tunnelling has also been observed for methane adsorbed on Sterling FT preplated with a monolayer of xenon. When a second layer of methane is added to the first the tunnelling spectrum becomes broad and an inelastic feature appears at higher energy corresponding to a slightly hindered rotation. The value of using tunnelling spectra of adsorbed species to test models of surface forces is discussed with examples of different atom—atom potential parameters.     

The state of metals in the Pt/Al2O3 and (Pt-Cu)/Al2O3 catalysts as indicated by IR spectroscopy with isotope dilution of 12C16O with 13C18O molecules

Adsorption of ¹³C¹⁸O+¹²C¹⁶O mixtures on the Pt(2.9%)/γ-Al₂O₃, (Pt(2.6%)+Cu(2.7%))/γ-Al₂O₃, and (Pt(2.6%)+Cu(5.1%))/γ-Al₂O₃ catalysts was studied by FTIR spectroscopy. On the metallic Pt surface at coverages close to saturation, CO is adsorbed both strongly and weakly to form linear species for which the vibrational frequencies of the isolated ¹³C¹⁸O molecules adsorbed on Pt are ∼1940 and ∼1970 cm⁻¹, respectively. The redistribution of intensities of the high-and low-frequency absorption bands in the spectra of adsorbed ¹³C¹⁸O indicates that these linear forms are present on the adjacent metal sites. The weak adsorption is responsible for the fast isotope exchange between the gaseous CO and CO molecules adsorbed on metal. The Pt-Cu alloys, in which the electronic state of the surface Pt atoms characteristic of monometallic Pt remains unchanged, are formed on the surface of the reduced Pt-Cu bimetallic catalysts. The decrease in the vibrational frequencies of the isolated C=O bonds in the isolated Pt-CO complexes suggests that the CO molecules adsorbed on the Cu atoms affect the electronic properties of Pt. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–836, May, 2007.     

Heterodyne measurements of hot bands and isotopic transitions of N2O near 7.8 µm

Heterodyne frequency measurements are reported for absorption transitions of N₂O in the frequency range from 1257 to 1335 cm^?1. The measurements use a CO laser as a transfer oscillator whose frequency is measured directly against combinations of frequencies of two stabilized CO₂ lasers whose frequencies are well known. A tunable diode laser is locked to the N₂O absorption feature and the frequency difference is measured between the diode laser and the CO laser. Thev ₃ fundamental bands of the¹⁵N¹⁴N¹⁶O and¹⁴N¹⁵N¹⁶O isotopes are reported. Measurements are also given for the 00⁰2–00⁰1, 02⁰1–02⁰0, and 02²1–02²0 vibrational transitions of N₂O. A table of frequencies is given for the 00⁰2–00⁰0 band near 2560 cm^?1 based on these and earlier measurements.     

The exciting oxidation of CO on Pt

An uncollimated molecular beam (free jet) of CO and O₂ molecules incident on a polycrystalline Pt surface at 775 K in vacuo produces vibrationally hot CO₂ molecules at a density sufficient for infrared emission spectrometry. Analysis of spectra at a resolution of 0.1 cm^?1 clearly shows that nascent product molecules have much more internal excitation than would be the case for equilibrium at the surface temperature.     

Simulated T ← S spectrum of 2,4,5-trimethylbenzaldehyde in durene

The T_1,2 ← S₀ phosphorescence excitation spectrum of 2,4,5-trimethylbenzaldehyde in durene has been simulated using forty-five zero-order Born-Oppenheimer product states of which thirty-two belong to T₁ (ππ*), the others to T₂ (nπ*). The spectrum is very complicated in the region 400–600 cm^?1 above the T₁ (ππ*) ←3 S₀ origin band at 24150 cm^?1. In this tangled region conventional vibrational analysis is not useful. Several comments on the physical properties of the excited triplet states of 2,4,5-trimethylbenzaldehyde are given.     

Intramolecular vibrational state mixing in glyoxal by stimulated emission pumping spectroscopy

Stimulated emission pumping spectra of glyoxal in a supersonic jet were recorded up to 7000 cm⁻¹ above the ground vibrational state employing X̃(¹A_g) ← Ã(¹A_u)2¹₀ vibronic transitions. At low energies, only isolated states were observed. However, at high energies, clumps of eigenstates were observed, which suggests extensive vibrational state mixing with dense bath states.     

Photolysis and Thermolysis of Pyridyl Carbonyl Azide Monolayers on Single‐Crystal Platinum

The photochemical and thermal reactivity of a number of acyl azide‐substituted pyridine compounds, namely nicotinyl azide, isonicotinyl azide, picolinyl azide and dinicotinyl azide with investigated as saturated monolayers on a single‐crystal Pt(111) surface in an ultrahigh vacuum chamber. Multilayers of the substrates exhibited a maximum rate of desorption at 270 K, above which, stable saturated monolayers formed as characterized by reflection‐absorption infrared spectroscopy by observation of C=O and N₃ bands at 1700 cm^?1, and 2100 and 1300 cm^?1 respectively. The monolayers were stable up to 400 K. Photolysis of the monolayer (or heating above 400 K) results in the formation of the respective isocyanate intermediate after loss of nitrogen as evidenced by the appearance of a new infrared band at 2260 cm^?1 with concomitant loss of the azide bands. The resulting isocyanate saturated monolayer is stable in absence of nucleophiles, but can be quenched with appropriate nucleophiles.     

Photoionization electronic spectroscopy of AlNa

Two electronic transitions are observed for a new heteronuclear dimer, AlNa, using two-color two-photon ionization spectrocopy (2R2PI). The combination of the analysis of vibronic structure and ab initio calculation enables us to assign the two transitions as D ¹Π←X ¹Σ⁺ and C ¹Σ⁺←X ¹Σ⁺; the origins of the D and C states are located at 16427 and 15422 cm⁻¹, and the vibrational frequencies being 151 cm⁻¹ in the D state, 115 cm⁻¹ in the C state, and 186 cm⁻¹ in the X state, respectively.     

Infrared Spectroscopic Studies on the Surface Chemistry of High‐Surface‐Area Gallia Polymorphs

Polymorphs α, β, and γ of Ga₂O₃ having hexagonal (corundum‐type), monoclinic and cubic (spinel‐type) structure, respectively, were prepared in a high‐surface‐area form, and characterized by powder X‐ray diffraction. Nitrogen adsorption at 77 K showed these gallia samples to have specific surface areas of 77 (α‐Ga₂O₃), 40 (β‐Ga₂O₃) and 120 m² g^?1 (γ‐Ga₂O₃). Fourier transform infrared spectroscopy of adsorbed carbon monoxide (at 77 K) and pyridine (at room temperature) showed that the three gallia polymorphs have a very similar surface Lewis acidity, regardless of their different crystal structures. This Lewis acidity was assigned, mainly, to coordinatively unsaturated tetrahedral Ga³⁺ ions situated on the surface of the small crystallites which constitute the different metal oxide varieties. Ga³⁺···CO adducts formed after CO adsorption gave (in all cases) a characteristic C–O stretching band at 2195–2200 cm^?1, while Lewis‐type adducts formed with adsorbed pyridine were characterized by IR absorption bands at 1610–1612 and 1446–1450 cm^?1. The three (partially hydroxylated) gallia polymorphs showed also a very weak Brønsted acidity, which they manifested by forming hydrogen‐bonded adducts with both CO and pyridine; however no protonation of adsorbed pyridine occurred.     

IR Studies of Coordinatively Unsaturated Surface Compounds on Silica Gel. IV. CO Complexes of Chromium(II) and Chromium(III)

Three different chromium(II) surface compounds have been identified by their IR spectra of adsorbed CO. Especially important in the interpretation of the experiments are the bands between 2050 and 2035 cm^?1 and the relative intensities of the CO bands at 2100 and 2120 cm^?1. The bands between 2192 and 2179 cm^?1 show also a different pattern for each of the different chromium(II) surface compounds. Two chromium(III) surface compounds could be identified by the presence of either one CO band near 2200 cm^?1 or two bands near 2206 and 2196 cm^?1. Three models are proposed for the chromium(II) title compounds, all related to dinuclear chromium(II) surface complexes: Models one and two have chromium(II) ions with trans and cis configuration in different combinations, respectively, and the third model has a bridging oxygen ion from a siloxan group as a distorting ligand. The three models explain the CO absorptions sufficiently and one is nearly quantitatively in agreement with previous volumetric adsorption studies of CO on chromium(II), which showed the surprising effect of decreasing CO adsorption with decreasing temperature. Two models for the chromium(III) surface compounds are proposed with either an oxygen double bridge or only one bridging oxygen.     

Vibrational spectroscopy of Cs+ solvated by methylamine

We report the vibrational spectra of the cluster ions Cs⁺(CH₃NH₂)_N, N=3–22. Bands in the 1015–1050 cm^?1 region of the infrared are due to the v8 mode (CN stretch) of methylamine molecules displaying different degrees of interaction with the central ion. Monte Carlo simulations of the solvated Cs⁺ ion indicate that nine methylamine molecules fill the first solvation shell of Cs⁺ and that possible rearrangements in cluster structure occur at N=14?15. No absorptions due to bulklike methylamine molecules are observed through N=22.     

The CO stretch frequency of fully CO covered Ag-clusters in dependence on cluster size

Silver clusters Ag_n prepared either by the gas aggregation technique (GAT) or by matrix aggregation of Ag were embedded in CO and CO/Ar-matrices. The vibrational CO stretch frequency at the monolayer coverage, which is found on bulk silver at 2110 cm^-1, preserves its value with decreasing particle size, Ag_n n≥300. For smaller clusters a decrease of this frequency with decreasing size was observed. For the smallest investigated clusters Ag_n, n～30, a value of 2080 cm^-1 was obtained. The weakening of the CO bond is an indication of a charge transfer from the cluster to the CO monolayer. This result is in accordance with the surface plasmon absorption measurements of Ag-clusters isolated in CO matrices.