Gas Phase Spectra Research Articles

Infrared spectra of (HCOOH)2 and (DCOOH)2 in rare gas matrices: A comparative study with gas phase spectra

Infrared absorption spectra of (HCOOH)(2) and (DCOOH)(2) in solid argon, krypton, and xenon matrices have been measured and each fundamental band has been assigned. Spectra in Ar and Kr matrices showed notable splitting in contrast to those in Xe, which suggests a difference in structure of the trapping sites. A comparison with the reported jet-cooled spectra has shown that vibrational structures of the spectra of (HCOOH)(2) and (DCOOH)(2) in the O-H stretching region are preserved in the matrices. On the other hand, the C-O stretching band of (HCOOH)(2) shows a drastic change upon matrix isolation, wherein the Fermi-triad feature observed in gas phase [F. Ito, Chem. Phys. Lett. 447, 202 (2007)] could not be identified. No substantial change of the vibrational structure has been found for matrix-isolated (DCOOH)(2). The differences of the vibrational structures in the matrix-isolation spectra and in the jet-cooled spectra have been qualitatively accounted for using the idea of anharmonic couplings among "matrix-shifted harmonic states."

X-ray absorption and resonant Auger spectroscopy of O2 in the vicinity of the O 1s→σ* resonance: Experiment and theory

We report on an experimental and theoretical investigation of x-ray absorption and resonant Auger electron spectra of gas phase O(2) recorded in the vicinity of the O 1s-->sigma(*) excitation region. Our investigation shows that core excitation takes place in a region with multiple crossings of potential energy curves of the excited states. We find a complete breakdown of the diabatic picture for this part of the x-ray absorption spectrum, which allows us to assign an hitherto unexplained fine structure in this spectral region. The experimental Auger data reveal an extended vibrational progression, for the outermost singly ionized X (2)Pi(g) final state, which exhibits strong changes in spectral shape within a short range of photon energy detuning (0 eV>Omega>-0.7 eV). To explain the experimental resonant Auger electron spectra, we use a mixed adiabatic/diabatic picture selecting crossing points according to the strength of the electronic coupling. Reasonable agreement is found between experiment and theory even though the nonadiabatic couplings are neglected. The resonant Auger electron scattering, which is essentially due to decay from dissociative core-excited states, is accompanied by strong lifetime-vibrational and intermediate electronic state interferences as well as an interference with the direct photoionization channel. The overall agreement between the experimental Auger spectra and the calculated spectra supports the mixed diabatic/adiabatic picture.

FT-IR, NIR-FT-Raman and gas phase infrared spectra of 3-aminoacetophenone by density functional theory and ab initio Hartree–Fock calculations

The gas phase infrared spectrum of 3-aminoacetophenone (3AAP) was measured in the range 5000–500 cm −1 and with a resolution of 0.5 cm −1. The Fourier transform Raman (FT-Raman) and Fourier transform infrared (FT-IR) spectra of 3AAP were recorded in the solid phase. Geometry optimizations were done without any constraint and several thermodynamic parameters were calculated for the minimum energy conformer at ab initio and density functional theory (DFT) levels invoking 6-311G(2df 2p) basis set and the results are compared with the experimental values. Harmonic-vibrational wavenumber was also calculated for the minimum energy conformer at ab initio and DFT levels using 6-31G(d,p) basis set and the results are compared with related molecules. With the help of specific scaling procedures, the observed vibrational wavenumbers in gas phase, FT-IR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range, the error obtained was in general very low. The appropriate theoretical spectrogram for the FT-IR spectra of the title molecule is also constructed.

Gas-phase ionisation of sputtered rare gas atoms

During bombardment of solid samples with rare gas ions, charge-transfer events can convert reemitted rare gas atoms to positively charged ions. In analytical applications of secondary ion mass spectrometry (SIMS) this mechanism of ion formation is of considerable interest because, owing to their high ionisation potential, the ion fraction of sputtered rare gas atoms is very low. A quadrupole-based SIMS instrument was used to study details of the gas-phase ionisation process, notably the variation of the ion production rate as a function of the distance from the surface. The relevant information was derived from the apparent energy spectra of gas-phase generated (GPG) ions, observed during bombardment of a variety of elemental targets with Ne +, Ar + and Kr + beams at energies between 3 and 12 keV. Owing to the use of a secondary ion extraction field of low strength, gas-phase ionisation events could be separated by distance δ from the surface, with δ up to about 6 mm. The results were compared with a simple model that describes the ion production rate as the product of the gas-atom flow rate and the ionisation probability. The first factor is proportional to the primary ion current and the second proportional to the current density j 0. Therefore, the intensity of GPG ions is not proportional to j 0 2 , as assumed previously. The mean ionisation probabilities of GPG ions (∼10 −5 at a moderate mean current density of ∼2 mA/cm 2) were found to be higher by more than four orders of magnitude compared to ‘ordinary’ SIMS. In part, this favourable result can be attributed to the low energy of rare gas atom ejection (∼0.1 eV). The experimental data suggest that the angular distributions of ejected rare gas atoms are strongly forward peaked. Presumably for this reason the yields of GPG ions observed with an amorphised target like silicon were distinctly higher than with polycrystalline metals. In the latter case, emission from unfavourably oriented microcrystals causes a large fraction of ejected gas atoms to escape from the interaction volume before ionisation can occur. Further enhancement in yield can be expected by the use of focussed primary ion beams with fairly uniform rather than Gaussian-like current density distributions. If the atomic number of the projectile is slightly lower than that of the target atom, as for Ne + impact on Mg, Al and Si or Ar + impact on Ti +, sizable or even high signals, independent of current density, were observed due to energetic multiply scattered ions.

Electronic structure of FeAl(1 1 0) using upgraded 6 m-TGM at CAMD

A new endstation has recently been commissioned at 6-m toroidal grating monochromator beamline to perform high-resolution photoemission studies in the photon energy range of 10–180 eV. The new endstation is equipped with Phoibos-150 analyzer with a channelplate and charge coupled device (CCD) camera readout to measure the kinetic energy of the electron and its emission angle simultaneously. The initial energy resolution test of the analyzer from He-I discharge lamp excited Argon 3p gas phase spectra reveals ∼20 meV full-width-half-maximum (FWHM). With this new set-up, we have investigated the electronic structure of FeAl(1 1 0). Preferential sputtering of clean FeAl(1 1 0) surface results in depletion of Al in the near surface region. The surface forms reconstructed phases at different annealing temperature regions. The electronic structure of these phases is presented.

Anharmonicity and tunneling effects in revisited vibrational O(1s) photoelectron spectrum of water gas phase

The authors have revisited the description of the core-hole ionization dynamics of the oxygen atom in water by re-exploiting the high-resolution, vibrationally resolved, XPS photoelectron spectrum of gas phase at the O(1s) edge. The agreement between theory and experiments is mainly controlled by (i) the description of the tunneling behavior near the barrier top (linear H-O-H conformation) of wave functions with high vibrational quanta, and (ii) the relative displacement of the potential-energy minimum of the O(1s) final state with respect to the ground state one. Accurate change in bond angle between the neutral and core-ionized states is essential to account for the Franck-Condon factors. The O(1s) photoelectron spectrum of water is well reproduced by the molecular ab initio calculations based on density functional theory and Franck-Condon factors calculations in a double-well (2 x W) simulation of the bending motion.

The vibrational spectrum of thiazole between 600 and 1400 cm −1 revisited: A combined high-resolution infrared and theoretical study

The Fourier transform infrared gas-phase spectrum of thiazole, C 3H 3NS, has been recorded in the 600–1400 cm −1 wavenumber region with a resolution around 0.0030 cm −1. Nine fundamental bands ( ν 5(A′) to ν 11(A′), ν 15(A″), and ν 16(A″)) are analysed employing the Watson model. Ground-state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from the fits. A detailed analysis of perturbations identified in the ν 11(A′) band at 866.5 cm −1 enables a definitive location of the very weak ν 10(A′) and ν 14(A″) bands at 879.3 and 888.7 cm −1, respectively. The three levels are analysed simultaneously by a model including Coriolis resonance using an ab initio predicted first order c-Coriolis coupling constant; second and higher order Coriolis parameters are determined. Qualitative explanations in terms of Coriolis resonances are given for a number of crossings observed in ν 5(A′), ν 6(A′), and ν 7(A′) at 1383.7, 1325.8, and 1240.5 cm −1, respectively. The rotational constants, anharmonic frequencies, and vibration–rotation constants (alphas, α ν A , B , C ) calculated by quantum chemical calculations using a cc-pVTZ and TZ2P basis with B3LYP methodology, have been compared with the present experimental data. The rotation constant differences for each vibrational state, from the ground state values, are closer to experiment from the TZ2P calculations relative to those using cc-pVTZ. The values for Δ J, Δ JK, Δ K, δ J, and δ K are close to experiment with both basis sets.

Gas phase and bulk photoemission spectra of highest occupied molecular orbitals of pi‐conjugated organic molecules

AbstractThe highest occupied molecular orbital (HOMO) of the pi‐conjugated organic molecule 3,4,9,10‐perylenetetracarboxylic dianhydride (PTCDA) was investigated via bulk and gas phase ultraviolet photoemission spectroscopy. As a result of the absence of various photoemission linewidth broadening effects which occur in the case of condensed matter, the measurements on single molecules allow an estimate of the contributions of these effects to the total linewidth. Distinctive peaks resulting from vibrational excitations can be recognized and thus a comparison with other spectroscopy methods is possible. Furthermore, spectra of the HOMOs of 1,4,5,8‐naphthalene‐tetracarboxylic dianhydride (NTCDA) and 1,8‐naphthalene‐dicarboxylic anhydride (NDCA) were also recorded and compared to the results for PTCDA, showing a decrease in linewidth with decreasing molecule size. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Solvent effects on the UV-visible absorption spectrum of benzophenone in water: A combined Monte Carlo quantum mechanics study including solute polarization

The entire ultraviolet-visible absorption spectrum of benzophenone in water is studied and compared with the same spectrum in gas phase. Five transitions are considered, and the corresponding solvatochromic shifts are obtained and compared to experiment. Using a sequential procedure of Monte Carlo simulations and quantum mechanical calculations, liquid configurations were generated and an averaged spectrum of the solution was calculated. The solute polarization was included by an iterative procedure where the atomic charges of the solute were obtained as an average with the solvent distribution. The calculated average dipole moment of benzophenone in water, with MP26-31++G(d,p), converges to the value of 5.84+/-0.05 D, 88% larger than the gas-phase value of 3.11 D. Using 100 statistically uncorrelated configurations and solvation shells with 235 explicit water molecules selected by a minimum-distance distribution of solvent shells, instead of the usual radial distribution, the excitation energies were obtained from solute-solvent all-valence-electron INDO/CIS calculations. The shift of the weak n-pi(*) transition is obtained as 2045+/-40 cm(-1) and the strong and broad pi-pi(*) shift as -1790+/-30 cm(-1). These results are in good agreement with the experimental values of 2200 and -1600 cm(-1), respectively. Standard procedure used by common force fields to generate atomic charges to describe the electrostatic moments of the solute, with HF6-31G(d), gives a dipole moment of 3.64 D. Using these standard charges in the simulation, the average shifts are calculated as 1395+/-35 and -1220+/-25 cm(-1), both about 600 cm(-1) smaller in magnitude than those obtained with the average converged fully polarized solute. The influence of the solute polarization in the solute-solvent interaction and, in particular, in solute-solvent hydrogen bonds is analyzed.

Spectroscopic Signatures of Halogens in Clathrate Hydrate Cages. 1. Bromine

We report the first UV-vis spectroscopic study of bromine molecules confined in clathrate hydrate cages. Bromine in its natural hydrate occupies 51262 and 51263 lattice cavities. Bromine also can be encapsulated into the larger 51264 cages of a type II hydrate formed mainly from tetrahydrofuran or dichloromethane and water. The visible spectra of the enclathrated halogen molecule retain the spectral envelope of the gas-phase spectra while shifting to the blue. In contrast, spectra of bromine in liquid water or amorphous ice are broadened and significantly more blue-shifted. The absorption bands shift by about 360 cm-1 for bromine in large 51264 cages of type II clathrate, by about 900 cm-1 for bromine in a combination of 51262 and 51263 cages of pure bromine hydrate, and by more than 1700 cm-1 for bromine in liquid water or amorphous ice. The dramatic shift and broadening in water and ice is due to the strong interaction of the water lone-pair orbitals with the halogen sigma* orbital. In the clathrate hydrates, the oxygen lone-pair orbitals are all involved in the hydrogen-bonded water lattice and are thus unavailable to interact with the halogen guest molecule. The blue shifts observed in the clathrate hydrate cages are related to the spatial constraints on the halogen excited states by the cage walls.

Optical constant, molar absorption coefficient, and imaginary molar polarizability spectra of liquid hexane at 25 °C extended to 100 cm −1 and vibrational assignment and absolute integrated intensities between 4000 and 100 cm −1

The infrared refractive index, molar absorption coefficient and imaginary polarizability spectra of hexane presented in a previous paper are extended to 100 cm −1. The vibrational assignment and curve fit of the imaginary molar polarizability spectrum of liquid hexane are presented between 4000 and 100 cm −1. A total of 157 peaks are required to fit the imaginary molar polarizability spectrum. An excellent fit was obtained which has an R 2-value equal to 0.9997, the χ 2 is 0.082 cm 6 mol −2 and the RMS error is 0.0033 cm 3 mol −1. Also the area under the experimental spectrum and the fitted spectrum only differ by 0.08%, where the fit is larger. With the aid of ab initio calculations and the gas phase spectrum, the liquid phase fundamentals and integrated intensities have been assigned for most of the infrared active fundamentals, and the dipole moment derivatives with respect to normal coordinates and the transition moments are reported.

Fragment molecular orbital calculations on red fluorescent protein (DsRed)

We have performed the calculations of configuration interaction singles with perturbative doubles correction (CIS(D)) in conjunction with the multilayer fragment molecular orbital (MLFMO) scheme for a red fluorescent protein isolated from Discosoma coral (known as DsRed). The pigment geometry of DsRed was first examined by employing several model molecules whose spectra in gas-phase were actually observed, and an adequacy was confirmed. The excitation energy was then calculated to be 2.28 eV at the MLFMO-CIS(D)/6-31G ∗ level. The emission energy was also estimated to be 2.21 eV similarly. These theoretical values were in good agreement with the corresponding experimental values of 2.22 eV and 2.13 eV.

Morphology and electronic properties of the pentacene on cobalt interface

In this paper, we report the structural and electronic properties of pentacene thin films grown on a polycrystalline Co film using atomic force microscopy and ultraviolet photoemission spectroscopy (UPS), respectively. Investigation of this type of interface is of importance for the engineering of hybrid organometallic spintronic devices for which the use of spin polarized electrodes is a prerequisite. Uniform single crystalline areas of pentacene as large as several micrometers, with molecules arranging almost perpendicular to the substrate, were obtained. For the electronic properties at this interface, we have found an energy barrier for the hole injection of about 1eV, in spite of the fact that the ionization potential of pentacene reported previously equals the work function of Co. A shift of the vacuum level of the same magnitude has also been observed. A comparison of the UPS spectra of the pentacene films with the gas phase spectrum directly indicates that hybridization effects are present at this interface.

An ab initio and DFT study of structure and vibrational spectra of disiloxane H 3SiOSiH 3 conformers : Comparison to experimental data

The structural and vibrational properties of siloxane monomers may account in the physical and chemical properties of silicone polymers. Because disiloxane (H 3SiOSiH 3) is the smallest molecule in the set which runs through small siloxanes like hexamethyldisiloxane (CH 3) 3SiOSi(CH 3) 3 to silicone polymers, its energetic, structural and vibrational features have been investigated in detail using density functional theory (B3LYP), post Hartree-Fock methods (MP2 and CCSD(T)) and basis sets up to spdfg quality. Five conformations were considered: three bent structures with C 2v (double staggered, SS, and double eclipsed, EE, conformations) and C s symmetries, and two linear forms with D 3d and D 3h symmetries. At all levels of theory, the relative stability was C 2v(SS) ≈ C 2v(EE) > C s > D 3h > D 3d. The difference of energy between the two C 2v conformers is lower than 0.04 kcal/mol. At the highest level of theory (CCSD(T)/cc-pVQZ), the barrier to linearisation from C 2v to D 3h conformers was calculated at 0.43 kcal/mol, which is extremely low. Most of the structural and vibrational features of the disiloxane do not depend on the conformation of the molecule but are strongly influenced by the SiOSi angle. Anharmonic calculations allowed, without any scaling factor, an exhaustive reinvestigation of the assignments of observed wavenumbers in the infrared and Raman spectra of gaseous disiloxane. Particularly, in the gas phase spectrum, the SiOSi symmetric and antisymmetric stretches have been assigned at 599 and 1105, 596 and 1060, 527 and 1093 cm −1 for H 3SiOSiH 3, H 3Si 18OSiH 3 and D 3SiOSiD 3, respectively. The experimental wavenumber splitting of SiOSi symmetric and antisymmetric stretches of H 3SiOSiH 3 gave an estimation of the SiOSi angle at around 145°. Ab initio methods were revealed more accurate for structural parameters, when DFT/B3LYP was enough for spectral assignments, even at the harmonic level using a single scaling factor.

The electronic emission spectrum of SiB

The gas phase spectrum of the silicon boride radical has been observed for the first time. Two electronic transitions were observed in emission from a corona excited supersonic expansion source. The D 4Σ −– X 4Σ − system consists of emission from v′ = 0 to v″ = 0–3, while the A 4Π– X 4Σ − system consists of numerous bands with v′ = 0–5 and v″ = 0–11, although only the strong 0–0 and 0–1 bands have been analyzed so far.

The ultraviolet spectrum of condensed methylamine at 25 K

Using a monochromated synchrotron light source we have recorded the VUV spectrum of a film of solid methylamine, CH 3NH 2, from 6 to 10 eV. The solid-phase spectrum differs substantially from the gas-phase spectra with lower lying Rydberg states in the gas phase being absent in the solid phase. Vibrational structure visible in the gas phase is also absent in the solid phase. We suggest hydrogen bonding in solid CH 3NH 2 hinders the ν 9 NH 2 umbrella mode seen in the gas phase, instead a series of progressions in ν 6 (CH 3 umbrella) is observed.

Gas-phase detection of HSOD and empirical equilibrium structure of oxadisulfane

We present the first gas phase spectra of singly deuterated oxadisulfane, HSOD, in its vibrational ground state. More than 100 transitions have been recorded with highest frequency accuracy using the Cologne Terahertz Spectrometer. The molecular parameters derived from a least squares fit analysis proof HSOD to be an almost accidental symmetric prolate top molecule with an asymmetry parameter κ=−0.9985. Spectra of c-type and weaker b-type transitions have been recorded in the range from 716 to 772 GHz. The ratio of the dipole moments μ c/ μ b=2.4(3) has been derived from measured line intensities. The c-type transitions are split by the tunneling motion of a hindered internal rotation, whereas b-type transitions show no splitting within the Doppler limited line profiles. We derived the equilibrium molecular structure of oxadisulfane, HSOH, from experimental values of the rotational constants A 0, B 0, and C 0 of HSOH, H 34SOH, DSOD, and HSOD. The equilibrium rotational constants A e, B e, and C e were derived by taking vibration–rotation interaction constants α r obtained from high-level ab initio calculations into account.

The electron-stimulated desorption ions from the ionizer of a quadrupole mass spectrometer

The species and the pressure dependence of the electron-stimulated desorption (ESD) ions from the grid surface of the ionizer of the quadrupole mass spectrometer were measured by the QMS with the Bessel-box-type energy analyzer (BB-QMS). The BB-QMS was developed in order to measure true mass spectra of gas phase without ESD ion effect in high to extreme high vacuum. The ESD ions observed in typical residual gasses such as water, carbon monooxide, oxygen and carbon dioxide were H + (H 2O), O + (H 2O, CO, O 2, CO 2), OH + (H 2O). The intensity of the ESD ion signals showed saturation upon increasing coverage of the water molecules on the grid surface.

Electronic and Vibrational Spectroscopy and Vibrationally Mediated Photodissociation of V+(OCO)

Electronic spectra of gas-phase V+(OCO) are measured in the near-infrared from 6050 to 7420 cm(-1) and in the visible from 15,500 to 16,560 cm(-1), using photofragment spectroscopy. The near-IR band is complex, with a 107 cm(-1) progression in the metal-ligand stretch. The visible band shows clearly resolved vibrational progressions in the metal-ligand stretch and rock, and in the OCO bend, as observed by Brucat and co-workers. A vibrational hot band gives the metal-ligand stretch frequency in the ground electronic state nu3'' = 210 cm(-1). The OCO antisymmetric stretch frequency in the ground electronic state (nu1'') is measured by using vibrationally mediated photodissociation. An IR laser vibrationally excites ions to nu1'' = 1. Vibrationally excited ions selectively dissociate following absorption of a second, visible photon at the nu1' = 1 <-- nu1'' = 1 transition. Rotational structure in the resulting vibrational action spectrum confirms that V+(OCO) is linear and gives nu1'' = 2392.0 cm(-1). The OCO antisymmetric stretch frequency in the excited electronic state is nu1' = 2368 cm(-1). Both show a blue shift from the value in free CO2, due to interaction with the metal. Larger blue shifts observed for complexes with fewer ligands agree with trends seen for larger V+(OCO)n clusters.

The Gas Phase Spectrum of Cyclic C18and the Diffuse Interstellar Bands

The gas phase spectrum of the cyclic C18 molecule recorded in the laboratory at a temperature typical of diffuse interstellar clouds is compared with absorption features toward ζ Oph and HD 204827 in the 5730-5934 A region. For the origin band at 5928.5 A an upper limit to the column density of ≤1.8 × 1011 cm-2 is inferred. The origin band pattern in the laboratory spectrum changes on lowering the internal temperature in the 100-20 K range and bears a striking resemblance to the observed structure of a number of DIBs at other wavelengths. This suggests that platelike molecules or ions, comprising a couple of dozen to hundred carbon atoms, could be responsible for some of the latter absorptions.