Resonance Window Research Articles

Complexes of oxygen with benzene and hexafluorobenzene

The complexes of C6H6⋅O2, (C6H6)2O2, and C6F6⋅O2 were studied by photoionization using synchrotron radiation. Dissociation energies were measured to be D0(C6H6⋅O2)=1.6±0.3 kcal mol−1, D0[(C6H6⋅O2)+]=3.4±0.3 kcal mol−1, D0(C6F6⋅O2)=2.1±0.4 kcal mol−1, and D0[(C6F6⋅O2)+]=3.2±0.4 kcal mol−1. We calculate from the above that D298(C6H6⋅O2)=0.4±0.4 kcal mol−1, verifying that the benzene–oxygen interaction is only a ‘‘contact’’ at room temperature. The dissociation energies of the heterodimer ions are much smaller than those of the homodimer ions of their constituents [viz. 15, 11, and 7 kcal mol−1 for (C6H6)+2, (O2)+2, and (C6F6)+2. ] Sharp onsets were observed for C6H6⋅O2→(C6H6⋅O2)+ and C6F6⋅O2→(C6F6⋅O2)+, at 9.172±0.004 and 9.856±0.003 eV, respectively, measurements made possible by autoionization in the threshold region. Surprisingly, the heterodimer ion (C6H6⋅O2)+ is formed essentially entirely from neutral C6H6⋅O2, with no contribution from fragmentation of larger clusters. Production of C6H6O+ and C6F6O+ from C6H6⋅O2 and C6F6⋅O2 could not be detected, but is easily observed from mixed trimers. The first onsets occur at 14.10±0.05 and 14.10±0.09 eV, respectively, and are markedly higher than the thresholds. A second onset for C6F6O+ occurs at 14.7–15.0 eV. In addition, dips are observed near 590 Å in the yield spectra for both C6H6O+ and C6F6O+, where the well-known window resonances of the oxygen (c 4Σ−u)3sσg Rydberg states occur. Thus there is evidence for the participation of two different mechanisms. The former data are consistent with a mechanism in which the organic moiety is first photoionized to produce an excited ion that then dissociates the oxygen, where one of the oxygen atoms is captured by the ion. The latter data support a mechanism in which the O2 moiety is the chromophore, where O+, formed by predissociation of [O+2]* from autoionization of a Rydberg state, is captured by a benzene molecule. In either case, the product is born excited, and to be observed must be stabilized by excitation and ejection of the third component of the original trimer.

Photoionization of As2 and As4: Implications for group V clusters

The vacuum ultraviolet photoionization mass spectrum of As4 is presented, from the ionization threshold to 600 Å. The apparent adiabatic ionization potential is ≤8.49 eV, but the true value may be significantly lower. Three broad autoionization features are observed, probably comprising members of a Rydberg series converging to the B̃ 2A1 state of As+4. The first fragment, As+3, has an appearance potential (0 K) of 11.23±0.05 eV, from which we extract ΔH0f0(As+3)≤228.7±1.3 kcal/mol. The photoion yield curve of As+2(As2) is obtained under conditions where As2 is dominant in the vapor. The adiabatic ionization potential is 9.69±0.02 eV. Two prominent autoionizing Rydberg series are observed, converging to the A 2Σ+g state of As+2, with an ionization potential of 10.238±0.002 eV. At higher energy, three members of a window resonance series can be seen, converging to the B 2Σ+u state of As+2, with an ionization potential of 15.37 eV. From an upper limit to the partial pressure of As3, equilibrium conditions, and assuming a triangular As3, we deduce ΔH0f0(As3)≥60.0 kcal/mol; other criteria suggest ΔH0f0(As3)≂63 kcal/mol. Consequently, the adiabatic ionization potential of As3 is <7.32 eV, and probably ≤7.19 eV. Several implications are drawn, relevant to recent studies of antimony and bismuth clusters.

R-matrix calculation of atomic hydrogen photoionization in a strong magnetic field.

We describe atomic hydrogen diamagnetism within the framework of multichannel quantum-defect theory using an R-matrix approach. The calculated photoionization spectrum in the range of magnetic field B=${10}^{3}$--${10}^{4}$ T shows that the quasi-Landau resonances are broad interlopers that perturb high Rydberg states converging to the Landau thresholds, forming complex resonances. A partial-cross-section analysis indicates that electron population of different Landau channels depends on the azimuthal quantum number and parity of the final states. For odd-total-parity final states with m=1, the photoionized electron is predicted to escape predominantly in the higher Landau channels, while for final states with m=0, it escapes in the lower channels. This property is reflected in the shape of autoionizing resonances, which are more like peaks for m=1, but are more like dips (window resonances) for m=0.

Photoionization cross section of lead near the 6s26p 2P3/2 threshold.

Measurements of the total photoionization cross section of lead in the energy range between the 6${\mathit{s}}^{2}$6p${(}^{2}$${\mathit{P}}_{1/2}$) ionization threshold at 59 819 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and the 6${\mathit{s}}^{2}$6p${(}^{2}$${\mathit{P}}_{3/2}$) threshold at 73 900 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ are reported. Just above the ionization threshold the cross section is dominated by broad window resonances, members of the 6pnd and 6pns Rydberg series converging to the 6${\mathit{s}}^{2}$6p${(}^{2}$${\mathit{P}}_{3/2}$) threshold. The Rydberg series are perturbed by a very broad and intense autoionizing resonance near the threshold. The resonance energy, width, and shape parameter of this resonance are determined. Close to the 6${\mathit{s}}^{2}$6p${(}^{2}$${\mathit{P}}_{3/2}$) series limit the data indicate the presence of a further broad-window-type resonance.

Observation of autoionizing Rydberg series converging to SO+3(2E′,2A′1)

The ionization energy of SO3 is determined to be 12.828±0.010 eV from photoionization mass spectrometric measurements of SO3. Two autoionization Rydberg series converging to the SO3(2E′) state (17.901 eV) are identified. Three window resonances observed in the region 610–690 Å are assigned as members of an autoionizing Rydberg series converging to the SO+3(2A1) state (20.603 eV).

Jet-resolved vibronic structure in the higher excited states of N2O: Ultraviolet three-photon absorption spectroscopy from 80 000 to 90 000 cm−1

Ionization-detected ultraviolet multiphoton absorption spectroscopy reveals Rydberg structure in the excited states of N2O within 20 000 cm−1 of the first ionization threshold. This structure persists, with atomic-like quantum defects and vibrational structure well matched with that of the ion, despite evidence for coupling of vibrationally excited Rydberg states with the underlying valence continuum. In the most completely resolved spectrum, which is assigned to the 3pσ 1Π state, hot-band, fundamental and overtone transitions involving the bending mode ν2, indicate Renner–Teller and Herzberg–Teller coupling of electronic and vibrational angular momentum. Vibronic intensities and positions suggest that these couplings can be regarded as properties of the N2O+ ion core, mirroring behavior manifested in the electronic emission spectrum of the ion. Window resonances are observed in the ionization-detected absorption spectrum above the four-photon ionization threshold, which are assigned to vibrationally excited Rydberg states that couple to competing continuua in which predissociation dominates Δv=−1 vibrational autoionization.

Measurement of the ionization potential of triatomic hydrogen.

The d Rydberg series of ${\mathrm{H}}_{3}$ converging to the lowest rotational level of ortho-${\mathrm{H}}_{3}^{+}$ has been detected for n values ranging from 27 to 100 using field ionization. The Rydberg molecules are prepared by photoexcitation from the long-lived species, ${\mathrm{H}}_{3}$ B\ifmmode \tilde{}\else \~{}\fi{}(2${\mathit{p}}^{2}$${\mathit{A}}_{2}$'', N=K=0), in its lowest vibrational level. Extrapolation of the Rydberg series yields an ionization potential of 29562.6\ifmmode\pm\else\textpm\fi{}0.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The amplitudes of the excitation spectra reveal the interaction between the ${\mathrm{H}}_{3}^{+}$ cores with ${N}^{+}$=1 and 3 via l uncoupling of the d electron, as well as window resonances from interlopers belonging to vibrationally excited ${\mathrm{H}}_{3}^{+}$ cores.

Photoionisation of atomic arsenic

The photoionisation spectrum of atomic arsenic prepared by successive abstraction reactions involving H atoms and AsH3, has been obtained from its ionisation threshold at around 1266.6 to 745 AA. A number of s-like and d-like autoionisation resonance series have been identified converging to 3P1 and 3P2 of As+. At least one of the d-like series is broad and asymmetric. In addition, at higher energies a deep window resonance series is seen, involving inner s-shell excitation to . . . (5S)np 4P states. The quantum defect for this series is in good agreement with recent Hartree-Slater calculations.

Photoionisation of atomic phosphorus

The photoionisation spectrum of atomic phosphorus prepared by successive abstraction reactions involving H atoms and PH3, is presented from its ionisation threshold to 765 A. Prominent autoionisation structure is observed between the fine-structure limits3P2-3P0 near the ionisation threshold. In addition, a window resonance series is seen, involving inner s-shell excitation to . . .(5S)np 4P states. Some systematic behaviour of resonance profiles and quantum defects in a series of atoms is discussed.

Momentum transfer dependence of the (6σ) 2 → (6σ, npπ) window resonances in N 2O

Scattered electron spectra of N 2O employing 200 eV electrons have been recorded in an energy loss regime of 17 to 21 eV corresponding to excitation out of the 6σ orbital. In this region, the shapes of the (6σ, npπ) window resonance series exhibit a strong variation over a scattering angular range of 3 to 9°. For the n = 3 member, this is attributed to a change in the resonance profile index from ~ −0.2 to +0.9. Although profile index sign reversals have been measured in ejected electron spectra, their interpretation is difficult. The scattered electron aspect of our measurement lends itself to a more straightforward interpretation as a sign reversal in the transition amplitude for excitation to the modified discrete state, and our measurements provide one of the first clear-cut examples of this effect.

Photoionisation of atomic selenium

The photoionisation spectrum of atomic selenium, prepared by the reaction of H atoms with H2Se, is presented from its ionisation threshold to 600 AA. Autoionisation peaks assigned to quasidiscrete levels . . .(2D degrees )nd 3p degrees are sharp, those assigned to . . .(2D degrees )ns 3D degrees and . . .(2D degrees )nd 3S degrees are somewhat broader, and others assigned to . . .(3D degrees )nd 3D degrees are very broad. A few members of the series converging to Se+(2P degrees ) are also observed. Two prominent peaks are tentatively assigned to 4s4p5 3P degrees 2,1, and taken to be the first members of the series . . . 4s4p4np, the latter appearing as window resonances in this spectrum. The photoionisation spectrum of H2Se is also presented.

Molecular beam photoionization study of S2

Higher resolution photoionization efficiency data for the formation of S+2 and S+ from S2 in the wavelength region of 600–1350 Å have been obtained using the supersonic oven beam method. The ionization energy (IE) of S2 is determined to be 9.356±0.002 eV (1325.2±0.3 Å). The measured appearance energy of 14.732±0.005 eV (841.6±0.3 Å) for the dissociative ionization process S2+hν→S++S+e−, together with the IE of S2, yields a value of 5.376±0.005 eV for the bond dissociation energy of S+2. Two Rydberg series converging to the b̃ 4Σ−g state (13.20 eV) of S+2 are observed. Window resonances resolved in the wavelength region of 670–850 Å are assigned as members of the Rydberg series converging to the c̃ 4Σ−u (17.70 eV) and 2Πu (or 2Σ−u) (18.66 eV) states of S+2.

Autoionization in N2O as measured by angle-resolved photoelectron spectroscopy

Angle-resolved photoelectron spectroscopy has been carried out on N2O as a function of photon energy from 13.5 to 20.5 eV using monochromatized synchrotron radiation. The purpose of these studies has been to investigate autoionization, and most of the data have been collected under conditions of constant ionic state. Six resonances are discussed in detail: the first four that form a portion of several Rydberg series leading to the A 2Σ+ ionic state and the first two window resonances leading to the C 2Σ+ state. Data have been taken as a function of the final state vibrational band and as a function of angle between the ejected photoelectron and polarization vector. In particular, the correlation between the integrated angular intensity and its angular distribution parameter, β, has been measured as a function of photon energy over the resonances. The nature of these results and importance to the understanding of autoionization in molecules is discussed.

Inner-valence shell photoionization of Ar2, Ar3, Kr2, and Kr3

The inner-valence shell photoionization spectra (420<λ<500 Å) of Ar2, Ar3, Kr2, and Kr3 have been obtained with a molecular beam apparatus using synchrotron radiation from the VUV storage ring at the National Synchrotron Light Source. The photoionization spectra exhibit regular series of window resonances which are closely associated with the ms→np Rydberg series in atomic Ar(m=3) and Kr(m=4). Vertical ionization potentials of the lowest ionic state in the molecular ms regions were obtained by series extrapolation and these were used to estimate the well depths in the Franck–Condon region and dissociation energies. Assignments of the observed Rydberg transitions were made by analogy with similar excitations in He2 and the group II and II B metal dimers. For Ar+2 and Kr+2, the observed structure is tentatively assigned to 1u (1Πu) and O+u (1Σu+) states which correlate with the ‘‘promoted’’ ndπg and ndσg series. Plausible assignments for the trimer spectra are also discussed.

Autoionization states of SO2

We report the assignments of five autoionizing states of SO2 in the 960–810 Å region. The experimental data used in the present analysis have been previously obtained by a molecular beam photoionization mass spectrometry. The observed vibrational progressions are tentatively assigned to the following Rydberg transitions: 4b2→3s, 4b2→3d, 7a1→3p, 7a1→3d, and 2b1→3p. The window resonance series previously reported [C.Y.R. Wu and D. L. Judge, J. Chem. Phys. 74, 3804 (1981)] in a photoabsorption measurement is confirmed in the photoionization efficiency curves of SO+2 and SO+.

Study of sulfur-containing molecules in the EUV region. II. Photoabsorption cross section of COS

Using synchrotron radiation as a continuum background, the absorption cross sections of COS have been measured using a double ion chamber. The cross sections range from 7 to 50 Mb in the 175–760 Å region. The window resonance series VII (and VII′) and IX (and IX′) are tentatively assigned as nsσ and npπ converging to the C̃ 2Σ+ ion state of COS+. A dip at about 846 Å, which possibly corresponds to the n = 3 member of the VII series, is found in the high resolution photoionization curves previously published [Eland and Berkowitz, J. Chem. Phys. 70, 5155 (1979); Ono et al., J. Chem. Phys. 74, 1645 (1981), and Delwiche et al., J. Chem. Phys. 74, 4219 (1981)]. Broad structures observed in the 580–650 Å region may be Rydberg series converging to the highly excited ion states which are yet to be resolved and analyzed.

Study of sulfur-containing molecules in the EUV region. I. Photoabsorption cross section of SO2

Using synchrotron radiation as a continuum background, the absorption cross sections of SO2 have been measured using a double ionization chamber. The cross sections range from 10 to a maximum value of 56 Mb in the 175–760 Å region. A possible window resonance series was observed and tentatively assigned to a Ryberg series converging to the (6a1)−1 ion state. From the fluorescence excitation function the vibrational progressions of the SO+2 ? 2B2, ? 2A1, and ? 2B1 ion states have been measured and found in good agreement with those observed from photoelectron spectroscopy. The same correspondence between peaks in the fragment fluorescence excitation function and the photoelectron spectrum suggests that these ion states of SO2 are dissociative in nature.

Resonant window in a rectangular waveguide and its application for checking the parameters of an insulator

Resonant window in a rectangular waveguide and its application for checking the parameters of an insulator

Rays in magneto-ionic theory-II

In a homogeneous magnetoplasma the refractive index is given by the dispersion relation, which assumes that the angle between the wave normal and the superimposed magnetic field is known. But a radio signal travels along a path known as a “ray” whose direction is in general different from the wave normal, and in many problems it is the ray direction that is known and the wave normal direction is at first unknown. In a previous paper, for a plasma in which the only effective carriers are electrons, a formula was given for finding the refractive indices when the ray direction is given. In this paper the formula is extended to allow for the presence of heavy ions. It is an equation of degree six whose solutions are associated with six different waves, although not all of them are necessarily excited by a given source. The properties of the equation are illustrated by discussion of its solutions at cut-off frequencies and resonance frequencies, and by showing its connection with resonance cones, Storey cones, and window points. A specific example of a plasma containing protons and He + ions is studied as an illustration.

Étude Par Spectrométrie de Vibration, de L'Interaction Entre Les Halogénures de Trialkylammonium et Quelques Dérivés Phénoliques. II. Vibration vNH+

AbstractThe vibrational spectrum of Et3NH+ Cl− and Et3 N H+ Br− has been examined in the v NH+ range. In the solid state, the Raman spectrum shows a well‐defined doublet while the infrared band profile is very large and shows a resonance window fixed at 2510 cm−1. The same effect is observed for both salts dissolved in 1,2 dichloroethane. The formation of hydrogen bonded complexes between the anions Cl− or Br− and some phenol derivatives brings about a frequency shift of the vNH+ band toward higher wavenumbers. This shift depends on the acidity of the phenol derivative and on its concentration. For these complexes, a window also appears at 2510 cm−1; this negative absorption probably arises from a Fermi resonance with the rocking vibration of the methyl group.