High-resolution laser spectroscopy of H2 in a fast beam

High-resolution laser photofragment spectroscopy is performed in a fast beam of H₂c³Π_u⁻ formed by near resonant charge exchange. The observed linewidths allow partial resolution of the fine and hyperfine structure in the 1s3d g ³Σ⁺_g Rydberg state. Simulations of the spectra indicate that the hyperfine splittings are very close to those of H⁺₂ as expected for Rydberg states.     

Electron attachment and vibrational excitation in hydrogen iodide: calculations based on the nonlocal resonance model

High resolution laser spectroscopy has been applied to study the hyperfine structure of excited energy levels of Thulium I. As part of our aim to complete the fine and hyperfine structure of the Tm I spectra 51 transitions in the visible were measured and precise values for the magnetic dipole hyperfine structure constants A of 24 odd and 19 even levels were determined. In addition, a new energy level of even parity with J = 3/2 is found at 27 509.40 (5)cm^?1 using laser induced fluorescence spectroscopy.     

Photofragment spectroscopy of SO+ in the wavelength range from 308–514.5 nm

The direct photodissociation process SO⁺+hv→S⁺+O has been studied using the technique of ion photofragment spectroscopy. The kinetic energy distribution of the S⁺ photofragments has been measured for selected wavelengths in the range λ=308–514.5 nm. Transitions from the metastablea ⁴∏ state to the dissociative 1⁴∑⁺ state as well as from theX ²∏ ground state to a higher-lying²∏ state have been observed. From the vibrationally resolved kinetic energy spectra, the potential curve of the repulsive 1⁴∑⁺ state has been determined for the range of internuclear distancesR=3.0–4.5a ₀. In addition, the analysis gives the vibrational population of the SO⁺ (a ⁴∏) ions after dissociative electron-impact ionization of SO₂ in the low-pressure monoplasmatron ion source.     

The first two excited 1Σg+ states of Cs2

Laser-induced fluorescence Of Cs₂ molecules in the infrared region (4000–9000 cm^?1) has been observed using several exciting wavelengths from an argon-ion laser and from a ring dye laser. Accurate molecular constants for the first two excited ¹Σ_g⁺ electronic states are derived from spectra recorded at high resolution by Fourier transform spectroscopy. Main molecular constants are: (2)¹Σ_g⁺: T_c = 12114.090 cm^?1, ω_e = 23.350 cm^?1, B_c = 7.4.5 × 10^?3 cm^?1, R_c = 5.8316 Å; (3)¹Σ_g⁺: T_e = 15975.450 cm^?1, ω_e = 22.423 cm^?1 , B_e = 8.23 × 10^?3 cm^?1, R_c = 5.5569 Å.     

Isomeric molecular identification by UV laser photofragmentation

An apparatus is described which provides an alternative to collisional activation for distinguishing some selected isomeric molecular ions. A mass filter selects the molecular ion beam, which is crossed by the output of an excimer laser. Photofragmentation products are monitored by a magnetic sector mass spectrometer downstream of the interaction zone. Five criteria can be used to distinguish between isomeric molecular ions: (1) the photofragment mass spectra; (2) the normalized photogfragment intensities; (3) the kinetic energy spectra of the observed photofragments; (4) the dependence of criteria (1)–(3) on laser polarization; and (5) the dependence of criteria (1)–(4) on the laser wavelength. The scheme is applied to the isomeric pair HCO⁺−COH⁺. At 193 nm, decomposition into the products CO⁺ +H is barely endothermic for HCO⁺ but ca. 1.7 eV exothermic for COH⁺. The normalized intensity of CO⁺ from photofragmentation of a presumed COH⁺ target is found to be nine times that from an HCO⁺ target.     

Photofragment spectroscopy of N 2 + in the near UV

Photofragment spectroscopy of N ₂ ⁺ has been studied in the wavelength range 343–404 nm using an excimer-pumped dye laser with a spectral resolution of 0.2 cm^?1. The observed bands are assigned to transitions from thev″=23?26 levels of theX ²Σ _g ⁺ state to highlying rovibrational levels (v′≈46–48) of theB ²Σ _u ⁺ state, forming quasibound (predissociating) states above the dissociation limit N⁺(³ P)+N(⁴ S ⁰). Measurement of the photofragment kinetic energies allows to establish an absolute energy scale for the transitions with respect to the dissociation limit. Molecular constants for the lower and upper states of the observed transitions are determined. The measurements allow the first direct determination of the N ₂ ⁺ dissociation energyD ₀ ⁰ (N ₂ ⁺ ). Some high-resolution (0.04 cm^?1) measurements show the fine-structure splitting and lifetime broadening of the excitation lines.     

Intramolecular easily polarizable hydrogen bonds with anilides of 1-piperidine carboxylic acids

IR spectra are plotted from anilides of 1-piperidine carboxylic acids C₅H₁₀N(CH₂)_n CONHC₆H₄R in CHCl₃ and CDCl₃ solutions. In the cases of n = 1 and n = 4, weak intramolecular (NH?N) hydrogen bonds are formed. An asymmetrical energy surface occurs and the proton is present at the N of the anilide group. In the cases of n = 2 and n = 3, intramolecular proton transfer hydrogen bonds of the types N_BH?N_P ? ^?N_B?H⁺N_p are formed. In contrast to the intramolecular OH? N ? O^?1 ? H⁺N bonds with 1-piperidine carboxylic acids, these bonds to not cause IR continua but two bands: one in the region 3250–3190 and one in the region 2500–2450 cm^?1. The fact that, instead of IR continua, bands are observed is explained by the following: (1) these hydrogen bonds are relatively long; (2) they show only a narrow distribution of bond length; (3) the electrical fields at these bonds are small, since they are strongly screened.     

Kinetic energy spectra of N2+ photofragments in the laser photodissociation of N2O+

Using a ZAB-2F double-focusing mass spectrometer together with an argon-ion laser, the kinetic energy spectra of N₂⁺ photofragments from the photodissociation of N₂O⁺ have been measured at wavelengths 514.5, 496.5, 488.0 and 476.5 nm in the visible region of the spectrum. Energies released in the centre-of-mass frame of reference are given. From the results it is deduced that the states involved in the absorption and dissociation processes ar probably N₂O⁺(B̃²Π) v ⩾ 3 and N₂O⁺ (C̃²Σ⁺) v ⩾ 0, respectively.     

Molecular polarization and laser photopredissociation in the presence of a magnetic field

The theory of the angular distribution of the photofragment resulting from weak predissociation in a diatomic molecule is worked out in the density matrix formalism. Special attention is given to the relationship between photofragment anisotropy, molecular polarization and fluorescence light polarization. The effect of a steady applied magnetic field is discussed and compared with classical Hanle effect. Application to the case of O₂⁺, b⁴σ_R^? state studied by fast ion beam laser spectroscopy (FIBLAS) is presented. Zeeman effect of the low J levels is observed in good agreement with theory and the angular distribution of the photofragments arising from a few selected Zeeman sublevels offers qualitative experimental confirmation of the theoretically predicted behavior.     

Free-jet studies of the visible spectroscopy of some perhalonitrosomethanes

Recent work on the electronic spectroscopy of halogen substituted nitrosomethanes in the visible spectral region is reviewed with particular reference to laser-induced fluorescence and photofragment yield spectra in supersonic free-jet expansions. The A(n, π*)-X electronic spectra in the 650–720 nm region are dominated by progressions in low frequency torsional modes, that reflect eclipsed to staggered dihedral conformational changes upon electronic excitation. The observed torsional progressions can be understood well on the basis of spectral simulations that utilize a simple one-dimensional Hamiltonian for the hindered internal rotation. The relevance of these laser spectroscopic studies for current work on the state-selected photophysics and photodissociation dynamics of the title compounds is highlighted.     

Laser photoionization and spectroscopy of gas phase silver clusters

Silver clusters containing up to 40–50 atoms are produced by laser vaporization in a pulsed-nozzle molecular beam source and studied with laser photoionization mass spectroscopy. A variety of Nd:YAG pumped dye laser and UV excimer laser wavelengths are used to achieve ionization. Ionization dynamics are studied by varying the laser wavelength and fluence. Bracketing experiments under single-photon ionization conditions are used to estimate ionization potentials as a function of cluster size. An even-odd ionization potential alternation is observed with odd-numbered clusters (N=3, 5, 7 ...) having lower ionization potentials than adjacent even-numbered species. Shell closings at clusters containing 2, 8 20 and 40 electrons are observed consistent with a one-electron shell model picture of cluster electronic structure. Resonance-enhanced ionization produces a vibrationally resolved spectrum for the trimer, Ag₃, yielding an electronic state assignment and excited state vibrational frequencies. Fragmentation in dimer ionization via theE state at 249 nm establishes the dissociation energy of Ag ₂ ⁺ to be <2.1 eV.     

New Spectral Techniques: Time-Resolved Fourier-Transform Spectroscopy and Two-Color Laser-Induced Grating Spectroscopy

Time-resolved Fourier-transform spectroscopy and two-color laser-induced grating spectroscopy are two new techniques recently employed in this laboratory. We recorded emission in the near infrared region during laser photolysis of HONO₂ with a step-scan Fourier-transform spectrometer and achieved temporal resolution in the microsecond range and spectral resolution of 0.1 cm¹. Rotationally resolved emission lines of the (0,0) band of the D ²∑⁺ →A ²∑ ⁺ transition of NO in the region 8900-9300 cnv^?1 with irregular relative intensities were observed when an ArF excimer laser was used to photodissociate HONO₂. The spectroscopic parameters of both D ²∑⁺ and A ²∑⁺ states agree with those previously reported. When a narrow-band ArF laser was used, selective rotational levels of the D state of NO were populated depending on the wavelength of the ArF laser. Our results indicate that absorption of a 193-nm photon by NO(υ″ = 1) is responsible for the observed emission. To test the technique of two-color laser-induced grating spectroscopy, we employed the B ³II_0U⁺-X ¹∑_g ⁺ system of I₂. Background-free spectra with transitions involving rotationally selected states were recorded. Various experimental schemes were employed with population gratings formed in either the B or X state. Signals due to different four-wave mixing schemes were distinguished by variation of relative timing between the grating beams and the probe beam.     

Homoleptic Zinc(II) Complexes Based on 4′‐(2‐Thienyl)‐terpyridine: Preparation,Structures, and Properties

The homoleptic complexes Zn^II(4′‐(2‐(5‐R‐thienyl))‐terpyridine)₂(ClO₄)₂ [R = hydrogen ( 1 ), bromo ( 2 ), methyl ( 3 ), and methoxy ( 4 )] were prepared. Their structures were determined by single‐crystal X‐ray diffraction analyses, and further characterized by high resolution mass, infrared spectra (IR), and elemental analyses. Single crystal X‐ray diffraction analysis showed that Zn^II ions in the complexes are both six‐coordinate with N₆ coordination sphere, displaying distorted octahedral arrangements. The absorption and emission spectra of the homoleptic Zn^II complexes were investigated and compared to those of the parent complex Zn^II(4′‐(2‐thienyl))‐terpyridine)₂(ClO₄)₂. The UV/Vis absorption spectra showed that the complexes all exhibit strong absorption component in UV region, moreover, complex 4 has an absorption component in the visible region. Thus, the photocatalytic activities of the complexes in degradation of organic dyes were investigated under UV and visible irradiation.     

Synthesis,structure, spectroscopic,and DNA binding properties of Co(III) and Ni(II) complexes with ((E)-2-(amino((pyridin-2-ylmethylene)amino)methylene)maleonitrile)

Two new complexes, [Co(L)₂]Cl·(MeOH)₂ (1) and [Ni(L)₂]₄·EtOH (2) (L?=?(E)-2-(amino((pyridin-2-ylmethylene)amino)methylene)maleonitrile), were synthesized and characterized by X-ray crystallography, IR, UV, and fluorescence spectroscopy. According to X-ray crystallographic studies, each metal was six-coordinate with six nitrogens from two ligands. Both complexes form two-dimensional supramolecular networks via hydrogen bonding and π–π interactions. Ultraviolet and visible spectra showed that absorptions arise from π–π ^?, MLCT, and d–d electron transitions. Fluorescence spectroscopy revealed moderate intercalative binding of these two complexes with EB–DNA, with apparent binding constant (K _app) values of 9.14?×?10⁵ and 3.20?×?10^5?M^?1 for Co(III) and Ni(II) complexes, respectively. UV–visible absorption spectra showed that the absorption of DNA at 260?nm was quenched for 2 but quenched then improved for 1 with addition of complexes, tentatively attributed to the effect of the combined intercalative binding and electrostatic interaction for 1.     

Direct photodissociation of SO+ via the 14Σ+ state

The direct photodissociation process SO⁺ a ⁴Π +hv → S⁺ (⁴S⁰) + O(³P) via the repulsive SO⁺ 1⁴Σ⁺ state has been studied using a laser-ion photofragment spectrometer with coaxial beams. The kinetic energy distribution of the S⁺ photofragments has been measured at a laser wavelength of λ=488 nm (hv=2.54 eV). The spectrum shows vibrational structure which can be assigned to transitions from the vibrational levelsv = 7–13 of the initiala ⁴Π state. The experimental data are used along with semi-empirical calculations to locate the potential curve of the repulsive 1⁴Σ⁺ state in the Franck-Condon region. The results are compared with data obtained from photopredissociation studies of SO⁺ and with theoretical calculations for the 1⁴Σ⁺ state.     

Multiphoton excitation of CS2 with a narrow-band KrF laser

Multiphoton excitation of CS₂ by means of a frequency-narrowed tunable KrF laser (248 nm) leads to ionisation and photofragment fluorescence from CS(A ¹Π) and CS(d³Δ). Emission spectra can be obtained without any interference from the strong laser-induced flourescence from CS(X¹Σ⁺) observed in previous work with broad-band KrF laser. Excitation and fragmentation mechanisms are discussed within the context of higher Rydberg states of CS₂.     

Bridge‐Localized HOMO‐Binding Character of Divinylanthracene‐Bridged Dinuclear Ruthenium Carbonyl Complexes: Spectroscopic,Spectroelectrochemical, and Computational Studies

The electronic properties of four divinylanthracene‐bridged diruthenium carbonyl complexes [{RuCl(CO)(PMe₃)₃}₂(μ? CH?CHArCH?CH)] (Ar=9,10‐anthracene ( 1 ), 1,5‐anthracene ( 2 ), 2,6‐anthracene ( 3 ), 1,8‐anthracene ( 4 )) obtained by molecular spectroscopic methods (IR, UV/Vis/near‐IR, and EPR spectroscopy) and DFT calculations are reported. IR spectroelectrochemical studies have revealed that these complexes are first oxidized at the noninnocent bridging ligand, which is in line with the very small ν(C?O) wavenumber shift that accompanies this process and also supported by DFT calculations. Because of poor conjugation in complex 1 , except oxidized 1⁺ , the electronic absorption spectra of complexes 2⁺ , 3⁺ , and 4⁺ all display the characteristic near‐IR band envelopes that have been deconvoluted into three Gaussian sub‐bands. Two of the sub‐bands belong mainly to metal‐to‐ligand charge‐transfer (MLCT) transitions according to results from time‐dependent DFT calculations. EPR spectroscopy of chemically generated 1⁺ – 4⁺ proves largely ligand‐centered spin density, again in accordance with IR spectra and DFT calculations results.     

Ion/molecule reactions,mass spectrometry and optical spectroscopy in a linear ion trap

A linear-geometry, radio-frequency, quadrupole ion trap has been developed to generate, purify, accumulate and study atomic and molecular ions in the gas phase. By employing a trap-based system, both reactant and product ions can be stored for significant time periods, which can both enhance the efficiency of gas-phase reaction processes and create an environment to observe collision products after vibrational and rotational excitations have had time to relax. Relaxation occurs via viscous cooling with a dilute buffer gas or via laser cooling. Furthermore, the setup is particularly useful for performing optical spectroscopy on the trapped ions.Atomic and molecular ovens are used to generate thermal beams of neutral species, which are then ionized by electron bombardment. The ions can be trapped, or they can be collided with neutral molecules (e.g. C₆₀) under well defined experimental conditions. The collision energies are variable over a range from nearly 0 to 200 eV. This feature makes possible studies of complex formation, charge transfer and collision-induced fragmentation as a function of kinetic energy. A wide range of masses of up to 4000 u can be stored and manipulated with this apparatus.Two mass spectrometric techniques for the analysis of trapped ionic species are presented. In one method, parametric excitation of the secular motion is used to generate mass spectra with resolutions as high as 1 part in 800 with a simple experimental setup. The second method is capable of quickly generating mass spectra over the entire range of trapped masses, but has only moderate resolution. These spectra are generated by linearly sweeping the rf-trapping voltage to zero and detecting ions as their trap depth falls below a threshold value. In the trapping volume, which is 10 cm in length and 200 μm in diameter, 10⁶ ions can be loaded and stored, corresponding to an ion density above 10⁸ cm⁻³. Such densities facilitate spectroscopy of the stored ions. Both laser-induced fluorescence and photodissociation measurements have been carried out with a cw laser system providing near-infrared, visible, and ultraviolet beams. Absolute, total cross-sections and branching ratios of the photodissociation of MgC⁺₆₀ have been measured.     

Evolved gas analysis–ion attachment mass spectrometric observation of Mn(CO)5 and Mn2(CO)9 radicals produced by Mn2(CO)10 pyrolysis

Evolved gas analysis?Cion-attachment mass spectrometry (EGA?CIAMS) indicates that Mn(CO)₅ and Mn₂(CO)₉ free radicals are produced in the gas phase by pyrolysis of Mn₂(CO)₁₀ in an infrared image furnace. The Li⁺-adduct mass spectra of the pyrolysis products contained peaks at m/z 202 and 369 for Mn(CO)₅Li⁺ and Mn₂(CO)₉Li⁺, respectively, providing direct evidence that d-metal complex radicals were formed in the furnace. We studied the effect of temperature on the rate of production of the radicals, and confirmed the presence of the compounds Mn(CO)₅ and Mn₂(CO)₉, which were reported in earlier studies based on electron-impact mass spectrometry, electron spin resonance spectroscopy, and Fourier transform infrared spectroscopy.     

Catechin mediated green synthesis of Au nanoparticles: Experimental and theoretical approaches to the determination HOMO-LUMO energy gap and reactivity indexes for the (+)-epicatechin (2S, 3S)

This work suggests a green method for synthesizing Au nanoparticles (AuNPs) using the aqueous extract of Salix aegyptiaca extract. The mechanism of green synthesized AuNPs was examined by molecular electrostatic potential (MEP) calculations. AuNPs were characterized with different techniques such as Ultraviolet–visible spectroscopy (UV–vis), Fourier-transform infrared spectroscopy (FT-IR) spectroscopy, X-ray diffraction (XRD), and Transmission electron microscopy (TEM). Electrochemical investigation of modified glassy carbon electrode using AuNPs (AuNPs/GCE) shows that the electronic transmission rate between the modified electrode and [Fe (CN)₆]^3?/4? increased. Process of oxidation, energy gap, and chemical reactivity indexes of the (+)-epicatechin (2S,3S) were investigated using electrochemical techniques (cyclic voltammetry (CV) and differential pulse voltammetry (DPV) as well as UV–Visible spectroscopy and compared with quantum mechanical calculations. DPV and CV were used to obtain HOMO energies of the (+)-epicatechin (2S,3S), an optical energy gap was obtained from the UV–Vis spectroscopy. Frontier molecular orbitals analysis (FMO) and reactivity indexes such as chemical hardness (?), electrophilicity (?), electronic chemical potential (μ), electron acceptor power (?⁺), electron donor power (?^?) were determined with functional theory (DFT) calculations. In summary, the HOMO energy obtained from the experimental analyses (E_HOMO (from DPV) = -5.24 eV, and E_HOMO (from CV) = -5.28 eV) has a relative agreement with the HOMO energy calculated by B3LYP/6–31 g (d, p) including the solvent effect (water) (E_HOMO (from B3LYP) = -5.75 eV). Also, UV–Vis spectroscopy gives the bandgap energy equal to 4.31 eV, while the 4.13 eV is calculated by TD-DFT-b3lyp/6–31 + g(d).