Showing papers on "Photoionization published in 1995"

Locally Optimally Emitting Clouds and the Origin of Quasar Emission Lines

Abstract: The similarity of quasar line spectra has been taken as an indication that the emission line clouds have preferred parameters, suggesting that the environment is subject to a fine-tuning process. We show here that the observed spectrum is a natural consequence of powerful selection effects. We computed a large grid of photoionization models covering the widest possible range of cloud gas density and distance from the central continuum source. For each line only a narrow range of density and distance from the continuum source results in maximum reprocessing efficiency, corresponding to "locally optimally emitting clouds" (LOCs). These parameters depend on the ionization and excitation potentials of the line and its thermalization density. The mean QSO line spectrum can be reproduced by simply adding together the full family of clouds, with an appropriate covering fraction distribution. The observed quasar spectrum is a natural consequence of the ability of various clouds to reprocess the underlying continuum, and can arise in a chaotic environment with no preferred pressure, gas density, or ionization parameter.

Coherent Laser Control of the Product Distribution Obtained in the Photoexcitation of HI

Abstract: Active control of the distribution of products of a chemical reaction was demonstrated by using a method based on the principle of quantum mechanical interference. Hydrogen iodide (HI) molecules were simultaneously excited above their ionization threshold by two competing pathways. These paths were absorption of three ultraviolet photons of frequency ω 1 and one vacuum ultraviolet photon of frequency ω 3 = 3ω 1 . The HI + and I + signals were modulated as the phase between the lasers was varied, with the HI + signal lagging by 150° ± 15°. A mechanism consisting of autoionization and predissociation is proposed.

Reaction of cl with vibrationally excited ch4 and chd3 : state-to-state differential cross sections and steric effects for the hcl product

Abstract: The mechanism for the reaction of atomic chlorine with vibrationally excited methane is investigated by measurement of correlated state and scattering distributions using the method of core extraction (see preceding paper). Laser photolysis of molecular chlorine creates monoenergetic chlorine atoms (≳98% Cl 2P3/2) that react with vibrationally excited methane molecules prepared by linearly polarized infrared laser excitation. The resulting HCl product population distributions are determined by (2+1) resonance‐enhanced multiphoton ionization (REMPI), and the differential cross section for each product rovibrational state is measured by core extraction. Approximately 30% of the product is formed in HCl(υ=1,J) with a cold rotational distribution; the remaining population is formed in HCl(υ=0,J) and is more rotationally excited. We observe a rich variation of the scattered flux that is dependent on the internal‐energy state of the product. The HCl(υ=1) product is sharply forward scattered for low J and becomes nearly equally forward–backward scattered for high J; the HCl(υ=0,J) product is back and side scattered. The reactions of Cl with C–H stretch‐excited methane (CH4) and C–H stretch‐excited CHD3 are found to have similar angular and internal‐state distributions. Observation of the spatial anisotropy of the HCl(υ=0, J=3) product shows that significant vibrational excitation of the methyl fragment does not occur.The measured spatial anisotropy is most consistent with a model in which backscattered HCl(υ=0, J=3) is formed in coincidence with slight methyl vibrational excitation and the forward‐scattered HCl(υ=0, J=3) is formed in coincidence with no methyl excitation. The approach of the attacking chlorine atom with respect to the C–H stretch direction can be varied by rotating the plane of polarization of the infrared excitation. A marked steric effect is observed in which Cl atoms approaching perpendicular to the C–H stretch preferentially yield forward‐scattered HCl(υ=1) product. On the other hand, the reaction is weakly dependent on the rotational quantum state of CH4(υ3=1,J), and on the rotational polarization. The data are consistent with a model that has a widely open ‘‘cone of acceptance’’ in which the impact parameter controls the internal‐state and scattering distributions of the HCl product.

Rings in above-threshold ionization: A quasiclassical analysis

Abstract: A generalized strong-field approximation is formulated to describe atoms interacting with intense laser fields. We apply it to determine angular distributions of electrons in above-threshold ionization (ATI). The theory treats the effects of an electron rescattering from its parent ion core in a systematic perturbation series. Probability amplitudes for ionization are interpreted in terms of quasiclassical electron trajectories. We demonstrate that contributions from the direct tunneling processes in the absence of rescattering are not sufficient to describe the observed ATI spectra. We show that the high-energy portion of the spectrum, including recently discovered rings (i.e., complex features in the angular distributions of outgoing electrons) are due to rescattering processes. We compare our quasiclassical results with exact numerical solutions.

Laser techniques in chemistry

Abstract: Fourier-Transform Non-linear Spectroscopies Near-Infrared Laser-Optothermal Techniques Direct Absorption in Supersonic Free-Jets High Resolution Optical Spectroscopy in the Ultraviolet Generation of Coherent Vacuum Ultraviolet Radiation: Applications to High-Resolution Photoionization and Photoelectron Spectroscopy Time-Resolved Resonance Raman in the Visible and Ultraviolet: Techniques and Applications Local Order and Ultrafast Dynamics in Liquids: Transient Grating Optical Kerr Effect Experiments Electric Field Effects in Molecular Systems Studied via Persistent Hole Burning Excited Electronic State Properties from Ground-State Resonance Raman Intensities Ultrafast Vibrational Spectroscopy: Methods, Theory and Applications.

Laser Ionization Mass Spectroscopy of Single Aerosol Particles

Abstract: We describe an instrument that measures the chemical composition of single aerosol particles. To facilitate detection of volatile species, particles are analyzed less than 0.5 ms after leaving ambient conditions and without touching any surfaces. Particles are introduced into a vacuum through a differentially pumped nozzle, then cross a He-Ne laser beam. The scattered light provides both size information and the trigger for an excimer laser that desorbs and ionizes molecules from the particle. Mass spectra with excellent signal to noise have been obtained from laboratory and ambient particles 0.3 to 16 μm diameter.

Dissociation, ionization, and Coulomb explosion of H + 2 in an intense laser field by numerical integration of the time-dependent Schrödinger equation

Abstract: The time-dependent Schr\"odinger equation for ${\mathrm{H}}_{2}^{+}$ in a strong laser field is solved numerically for a model that uses the exact three-body Hamiltonian with one-dimensional nuclear motion restricted to the direction of the laser electric field. The influence of ionization on possible stabilization against dissociation is investigated. Unexpectedly high ionization rates from high vibrational states, exceeding those of neutral atomic hydrogen, are found. The ionization rates as functions of the internuclear distance R were also calculated for fixed nuclei, and these exhibit two strong maxima at large R, which explain the full dynamical results. A series of peaks seen in the calculated proton energy spectra can therefore be interpreted as occurring preferentially at (i) turning points of laser-induced vibrationally trapped states, and (ii) at the ionization maxima that occur at large internuclear distances of ${\mathrm{H}}_{2}^{+}$.

Ionization Dynamics in Strong Laser Fields

Abstract: The behavior of atoms submitted to intense electromagnetic fields is a subject of wide interest and active research. Much of the knowledge in this field is provided by studying the ionization dynamics, the energy and momentum of the photoelectrons, and the spectrum of emitted photons. Multiphoton ionization (MPI) is the process by which an atom is ionized by simultaneous absorption of several photons. The number of photons absorbed is in general even larger than the minimum required by energy conservation. The excess energy can be transferred to the photoelectron whose energy spectrum is composed of a series of lines separated by the photon energy. This process is known as above-threshold ionization (ATI). Alternately, the electron can be recaptured, emitting a series of energetic photons at odd harmonic frequencies of the driving field, dubbed optical harmonic generation (OHG). The particular topics studied in this paper are: Transient Resonances and Excited State Population Trapping; Evolution from Multiphoton to Tunneling; Electron Energy Distributions; Effects of Rescattering on the Photoelectron Energy and Momentum; {open_quotes}Direct{close_quotes} Channel in Multiphoton Double Ionization; {open_quotes}Nonsequential{close_quotes} Channel in Tunneling Double Ionization; and Nonsequential Rate.

Detection of compact ultraviolet nuclear emission in liner galaxies

Abstract: Low-ionization nuclear emission-line regions (LINERs), which exist in a large fraction of galaxies, may be the least luminous manifestation of quasar activity. As such, they may make possible the study of the active galactic nucleus (AGN) phenomenon in the nearest galaxies. The nature of LINERs has, however, remained controversial because an AGN-like nonstellar continuum source has not been directly observed in them. We report the detection of bright (greater than or approximately = 2 x 10(exp -16) ergs/s/sq cm/A), unresolved (full width at half maximum (FWHM) less than or approximately = 0.1 sec) point sources of UV (approximately 2300 A) emission in the nuclei of nine nearby galaxies. The galaxies were imaged using the Faint Object Camera (FOC) on the Hubble Space Telescope (HST), and seven of them are from a complete sample of 110 nearby galaxies that was observed with HST. Ground-based optical spectroscopy reveals that five of the nuclei are LINERs, three are starburst nuclei, and one is a Seyfert nucleus. The observed UV flux in each of the five LINERs implies an ionizing flux that is sufficient to account to the observed emission lines through photoionization. The detection of a strong UV continuum in the LINERs argues against shock excitation as the source of the observed emission lines, and supports the idea that photoionization excites the lines in at least some objects of this class. We have analyzed ground-based spectra for most of the northern-hemisphere galaxies in the HST sample and find that 26 of them are LINERs, among which only the above five LINERs have a detected nuclear UV source.

Ni2 revisited: Reassignment of the ground electronic state

Abstract: Resonant two‐photon ionization spectroscopy was used to study jet‐cooled Ni2 produced by pulsed laser ablation of a nickel target in the throat of a supersonic nozzle using argon as the carrier gas. Spectral regions previously investigated using helium as the carrier gas were reinvestigated, and the improved cooling achieved was found to suppress transitions arising from an Ω=4 state that had been thought to be the ground state. Seven new vibronic progressions were assigned, with spectroscopic constants determined for the excited states. The predissociation threshold in Ni2 was reinvestigated, and a revised value for the binding energy is given as D○0(Ni2)=2.042±0.002 eV. The ionization energy of Ni2 was found to be 7.430±0.025 eV, and from this result and the revised bond dissociation energy of the neutral, the binding energy of the cation was calculated to be D○0(Ni+2)=2.245±0.025 eV. Similarly, D○0(Ni−2)=1.812±0.014 eV is obtained using D○0(Ni2) and the electron affinities of Ni and Ni2. Twenty bands w...

High resolution laser photoionization and photoelectron studies

Abstract: Partial table of contents: An Historical Introduction to Threshold Photoionization (T. Baer & P.-M. Guyon). High Resolution Spectroscopy with Photoelectrons: ZEKE Spectroscopy of Molecular Systems (K. Muller-Dethlefs). State-Resolved Photoionization Dynamics of Small Molecules Using Coherent VUV Radiation (R. Wiedman & M. White). VUV-ZEKE Photoelectron Spectroscopy: Final-State Interactions in Small Molecular Systems (F. Merkt & T. Softley). Rotationally Resolved Autoionization of Molecular Rydberg States (H. Lefebvre-Brion). Exploiting Polarization in the Study of Molecular Photoionization Dynamics (K. Reid & D. Leahy). ZEKE Studies with Picosecond Lasers (J. Knee). Physics of Near-Threshold States in Molecular Hydrogen (E. Eyler). Indexes.

The structure of Nb3O and Nb3O+ determined by pulsed field ionization–zero electron kinetic energy photoelectron spectroscopy and density functional theory

Abstract: The geometrical structures of the ground states of triniobium monoxide, Nb3O, and its cation, Nb3O+, have been determined by an experimental and theoretical study. Vibrationally resolved photoelectron spectra of an Nb3O cluster beam were obtained at 100 and 300 K using the pulsed field ionization‐zero electron kinetic energy technique. The spectra were simulated by calculating multidimensional Franck–Condon factors using the geometries and harmonic vibrational frequencies obtained from density functional theory for the minimum energy structures of the ion and neutral molecule. The rather remarkable agreement between the experiment and the simulated spectra establishes that Nb3O and Nb3O+ have planar C2v structures with the oxygen atom bridging two niobium atoms. These are the most complex transition metal cluster structures to date to be characterized by gas phase spectroscopic techniques.

Non-Equilibrium Photodissociation Regions: Ionization-Dissociation Fronts

Abstract: We discuss the theory of coupled ionization--dissociation fronts produced when molecular clouds are exposed to $\lambda < 1110$\AA\ radiation from hot stars. A steady, composite structure is developed, which generally includes an ionized outflow away from the cloud, an ionization front, a layer of photodissociated gas, a photodissociation front, and a shock wave preceding the photodissociation front. We show that the properties of the structure are determined by two dimensionless parameters, $\psi$ and $\delta$, and by the Alfv\'en speed in the preshock gas. For a broad range of parameters of interest, the ionization front and the hydrogen photodissociation front do not separate, the H$_2$ photodissociation and photoionization take place together, and a classical hydrogen ``photodissociation region'' (PDR) does not exist. We also show that even when a distinct photodissociation region exists, in many cases the dissociation front propagates too rapidly for the usual stationary models of PDRs to be applicable. We discuss several famous PDRs, e.g., in M17 and Orion and conclude that they cannot be described by equilibrium PDR models.

Pulsars with strong magnetic fields: polar gaps, bound pair creation and nonthermal luminosities

Abstract: Modifications to polar-gap models for pulsars are discussed for the case where the surface magnetic field, Bs, of the neutron star is strong. For B ~ 4 X 108 T, the curvature ,-quanta emitted tangentially to the curved force lines of the magnetic field are captured near the threshold of bound pair creation and are channelled along the magnetic field as bound electron-positron pairs (positronium). The stability of such bound pairs against ionization by the parallel electric field,. Ell' in the polar cap, and against photoionization is discussed. Unlike free pairs, bound pairs do not screen Ell near the neutron star. As a consequence, the energy flux in highly relativistic particles and high-frequency (X-ray and/or ,-ray) radiation from the polar gaps can be much greater than in the absence of positronium formation. We discuss this enhancement for (a) Arons-type models, in which particles flow freely from the surface, and find any enhancement to be modest, and (b) Ruderman-Sutherland-type models, in which particles are tightly bound to the surface, and find that the enhancement can be substantial. In the latter case we argue for a self-consistent model in which partial screening of Ell maintains it close to the threshold value for field ionization of the bound pairs, and in which a reverse flux of accelerated particles maintains the polar cap at a temperature such that thermionic emission supplies the particles needed for this screening. This model applies only in a restricted range of periods, P2 Pl.

Photoionization spectroscopy of yttrium clusters : ionization potentials for yn and yno (n=2-31)

Abstract: The photoionization spectra of yttrium clusters Yn, and their monoxides YnO have been recorded for n=2–31. As has been observed for other transition metal clusters, the vertical ionization potentials decrease rapidly yet nonmonotonically to ∼10 atoms, beyond which a more gradual decrease takes place. The ionization potentials of the cluster monoxides were found to be similar to those of the corresponding bare clusters except for n≤10 where differences of 0.1–0.3 eV were observed in some cases. The absence of magic numbers or odd–even alternations is taken as evidence that threshold photoionization occurs from a localized 4d orbital rather than a delocalized band derived from 5s valence electrons.

Metal abundances and ionization in quasar intrinsic absorbers

Abstract: This paper provides a general reference for deriving the ionizations and metal abundances for absorption-line clouds in photoionization equilibrium with a QSO spectrum. The results include a quan- titative assessment of the theoretical uncertainties and -rm lower limits on the metallicities when no ionization constraints are available. The calculations applied to the best available column densities for QSO intrinsic absorbers support previous studies; there is strong evidence for super-solar metallicities in broad absorption line (BAL) and at least some "" associated II absorption regions. Even in cases (z a B z e ) where the level of ionization is unknown (e.g., when only H I and C IV lines are measured), -rm lower limits on the metal abundances (C/H) imply for typical BALs and some absorbers. These Z Z Z _ z a B z e results support the independent evidence for high metallicities in QSO broad emission line regions. I argue that high gas-phase abundances, up to D10 can be expected in QSOs because of the normal Z _ , enrichment by stars in the cores of young, massive galaxies. ( Z 1011 M _ ) The measured column densities in intrinsic absorbers also indicate that the gas is usually optically thin in the H I Lyman continuum out to energies above at least the C IV and N V ionization edges (i.e., Z100 eV). The column density ratios often require a range of ionization states in the same absorber. Neighbor- ing systems (having similar redshifts and often blended spectroscopically) also usually require dif- z a B z e ferent ionizations or metal abundances. If the abundances are similar in neighboring systems, their ionization parameters must sometimes di†er by more than an order of magnitude, requiring a signi-cant range of densities and/or distances from the ionizing QSO. These results, and the overall levels of ioniza- tion, are not consistent with single-zone models of the UV line and X-ray continuum ("" warm II) absorbers. Subject headings: galaxies: abundances E galaxy: evolution E quasars: absorption lines E quasars: general

Near‐infrared femtosecond photoionization/dissociation of cyclic aromatic hydrocarbons

Abstract: Pulses of 780 nm light of duration 170 fs and power densities up to 3.8×1013 W cm−2 are used to study the photoionization/dissociation processes in the series of gas phase, cyclic aromatic hydrocarbons including benzene, naphthalene, phenanthrene, and anthracene. The near‐infrared ionization process leads to the production of intact molecular ions for all of the molecules studied. Measurements of the ion intensity as a function of laser fluence revealed the order of the ultrafast ionization process to be 8.0±0.1 for anthracene, 6.9±0.1 for phenanthrene, 8.5±0.1 for naphthalene, and 8.1±0.1 for benzene. The relative femtosecond photoionization cross section decreased from 1.0 for anthracene to 0.2 for phenanthrene to 0.1 for naphthalene to ∼0.005 for benzene. The relative order and cross section of the femtosecond ionization processes suggest that a field ionization mechanism is operative.

The ratio of cross sections for double to single ionization of helium by high energy photons and charged particles

Abstract: Data and analysis for the ratio of double to single ionization in helium is reviewed for impact by photons and charged particles. In the case of photoionization there are two processes, namely, (i) photoionization where the photon is annihilated, and (ii) Compton scattering where the photon is inelastically scattered. In the case of charged particle scattering the ratio of total cross sections tends toward an asymptotic high energy value of 0.26% which is well below the value observed for photons of 1.7% at photon energies between 2 and 12 keV. Theoretical relations between various ratios have been predicted and to some extent confirmed by observations.

Threshold dependence of laser‐induced optical breakdown on pulse duration

Abstract: A model for optical breakdown is presented, that takes the effects of avalanche ionization, electron–ion recombination, and electron diffusion into account. By assuming a rectangular temporal shape of the laser pulse, an analytical solution of the threshold parameters can be given. Especially, a square root dependence of the energy density on the pulse duration is found for pulse duration values between roughly 4 ps and 8 μs. The theory explains the results of several previous experiments investigating threshold parameters for a variety of target materials.

Analytic FITS for partial photoionization cross sections.

Abstract: We present a compact, uniform and complete set of analytic fits to the partial Hartree-Dirac-Slater photoionization cross sections for the ground state shells of all atoms and ions of elements from H to Zn (Z less-than-or-equal-to 30). Comparison with experiment and theory demonstrates generally high accuracy of the fits up to energies of 100 keV.

Atomic data for opacity calculations. XXIII. The aluminium isoelectronic sequence

Abstract: As a contribution to the international Opacity Project, large numbers of term energies, oscillator strengths and photoionization cross sections have been computed for Al-like ions of astrophysical interest (Al I, Si II, S IV, Ar VI, Ca VIII and Fe XIV), using an ab initio close-coupling approach in LS-coupling. Careful comparisons with previous theoretical and experimental work show that our collisional approach allows a systematic and accurate description of plunging configurations, series perturbations and cancellations typical of these three-valence-electron systems. Even for highly ionized systems such as Fe XIV, the neglect of relativistic effects introduces limited inaccuracies ( approximately 5%) in the average term energies, and the gross features of the distribution of oscillator strengths are accurately delineated. The main contribution of the present study lies in the volume of accurate new data made available to the public through the TOPbase atomic database: 1935 computed multiplets compared to 225 observed ones, 56242 oscillator strengths and photoionization cross sections from 1296 initial states.

Nondipolar asymmetries of photoelectron angular distributions.

Abstract: We have measured the nondipolar contribution to the Ar 1{ital s} photoelectron angular distribution over the 30{endash}2000 eV electron-energy range. The nondipolar interaction results in a forward or backward asymmetry with respect to the photon beam. The asymmetry is directed backward near threshold, is symmetric near 230 eV, and becomes increasingly forward directed at higher energies. The measured asymmetries are in excellent agreement with theoretical calculations, which include interference between the electric-dipole and electric-quadrupole photoionization amplitudes. {copyright} {ital 1995 The American Physical Society.}

Electron-molecule collisions at very low electron energies

Abstract: Recent experimental advances that allow study of electron-molecule collisions at electron energies extending down to a few mu eV are reviewed. The new capabilities they afford are illustrated by considering collisions with molecules that attach low-energy electrons and with targets that have permanent dipole moments. Two different experimental approaches are discussed. The first makes use of free electrons produced by near-threshold photoionization. The electron energy can be controlled by varying the photon energy and, with the use of lasers, photoelectron energy resolutions as low as approximately 50 mu eV can be achieved. Low-energy electron scattering processes can also be investigated using atoms in high Rydberg states. For sufficiently large values of principal quantum number n, the excited electron and core ion can be considered as independent particles and the atom viewed, in essence, as a microscopic low energy electron trap with the trapping potential provided by the core ion. Measurements with very high n atoms, n>or approximately=1000, permit study of electron-molecule interactions at electron energies down to approximately 4 mu eV. The use of Rydberg atoms with low-to-intermediate values of n to probe the dynamics of dissociative electron attachment is also discussed with emphasis on determination of the lifetime of the excited intermediate and on how the excess energy of reaction is distributed between internal and translational motions of the products. The creation of weakly bound negative ions in Rydberg atom collisions is described focusing on low-energy electron attachment to van der Waals clusters and the formation of dipole-bound negative ions.

A graphical unitary group approach to study multiplet specific multichannel electron correlation effects in the photoionization of O2

Abstract: We have implemented an efficient multichannel configuration–interaction complete‐active‐space (MCCI‐CAS) approximation to study electron–correlation effects in molecular photoionization. This approach is based on the graphical unitary group approach (GUGA) for computing matrix elements of the Hamiltonian and includes target relaxation, correlation, and polarization as well as correlation due to coupling between different asymptotic scattering channels. The statistical rule, which partitions the total cross section into multiplets by simple spin statistics, is easily derived in this formalism. The scattering equations are solved using the Schwinger variational method. We present multiplet specific results of a detailed MCCI‐CAS Schwinger study of the photoionization of molecular oxygen in the photon energy region of 12.3–20.4 eV, including up to four coupled electronic channels. Our results show the importance of using correlated target states. We have obtained all of the autoionization structure near threshold that has been assigned experimentally. In addition, we predict structure not yet resolved by experiment.

Time‐delayed two‐color photoelectron spectra of aniline, 2‐aminopyridine, and 3‐aminopyridine: Snapshots of the nonadiabatic curve crossings

Abstract: We present time‐delayed two‐color photoionization photoelectron spectra of aniline, 2‐aminopyridine, and 3‐aminopyridine seeded in a cold molecular beam. The molecules are prepared in their S1 electronic states by a picosecond UV laser pulse and ionized by a time‐delayed 200 nm probe pulse. The photoelectron spectrum is observed with a time‐of‐flight spectrometer. All time‐delayed spectra reveal only one product of the nonradiative relaxation process. Careful considerations of electronic and vibrational overlap propensity rules for the ionization step lead to the conclusion that the dominant nonradiative decay mechanism in these molecules is the intersystem crossing to a bath of vibrationally excited levels of the T1 electronic state. Our observations reveal no admixtures of T2 or higher triplet levels. The pathway of the nonradiative electronic relaxation in 2‐aminopyridine is found to be independent of the initially prepared vibrational states up to 1000 cm−1 of vibrational energy. We find no evidence o...

Two-color multiphoton ionization of atoms using high-order harmonic radiation.

Abstract: Laser-assisted single-photon ionization of an atomic system can be observed in the simultaneous presence of a strong low-frequency laser field and of one of its (weaker) high-order harmonics. Typical photoelectron spectra associated to such two-color processes are simulated via the numerical solution of the time-dependent Schroedinger equation, for a hydrogen atom in the presence of both fields. We address the question of the interplay between this laser-assisted process and above-threshold ionization. Our results show that new sets of two-color experiments can be performed at moderate laser intensities easily attainable by currently operated sources.

Coherent phase control of the photoionization of H2S

Abstract: Coherent phase control was demonstrated for a bound‐to‐continuum transition of a polyatomic molecule. Three UV photons of frequency ω1 and one vacuum ultraviolet (VUV) photon of frequency ω3=3ω1 simultaneously excited H2S above its ionization threshold. The parent ion, H2S+, and fragment ions, HS+ and S+, produced by absorption of additional photons, were observed. All three ion signals were modulated as the phase difference between the light fields was varied.

The vibrationally resolved participator Auger spectra of selectively excited C 1s(2σ)−12π1 vibrational states in carbon monoxide

Abstract: The fully vibrationally resolved participator Auger spectra originating from the decay of the C 1s(2σ)−12π1 resonance in CO are presented. The C 1s(2σ)−12π1 v’=0 resonance has been excited with a 75 meV monochromator bandpass, i.e., in Auger resonant Raman conditions, and the participator Auger spectrum observed. The C 1s(2σ)−12π1 v’=1 resonance is also excited and the corresponding participator Auger spectrum observed with a monochromator bandpass slightly larger than the inherent width. The results are compared to theoretical simulations using coherent lifetime‐vibrational interference theory which accounts for the details of the spectrum. We have observed an interference shift on the transitions to different vibrational sublevels in the final state. A high resolution C 1s photoelectron spectrum of CO is also presented. The lifetime width of the C 1s core–hole state is determined to be 97(10) meV, whereas the C 1s(2σ)−12π1 resonance is measured to have a width of 86(10) meV.