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1 Nov 1988

Volume 89, Issue 9, pp. 5363-5969

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High temperature photoelectron spectroscopy: A study of U, UO, and UO2

G. C. Allen, E. J. Baerends, P. Vernooijs, J. M. Dyke, A. M. Ellis, M. Fehér, and A. Morris

J. Chem. Phys. 89, 5363 (1988); http://dx.doi.org/10.1063/1.455587 (10 pages) | Cited 9 times

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The He i photoelectron spectrum of atomic uranium has been recorded in the vapor phase. Bands associated with metal (6d)−1, (7s)−1, and (5f)−1 ionizations were observed. The relative intensities of the (6d)−1 and (5f)−1 bands are consistent with computed relative cross sections at the He i energy, whereas the intensity of the (7s)−1 band is larger than expected from computed cross sections, implying enhancement of this feature by autoionization effects. HeI photoelectron spectra have also been recorded for the vapor above a heated equimolar UO2(s)@B:U(s) mixture. By studying the spectra obtained as a function of temperature, bands associated with UO and UO2 were identified and these were assigned using relativistic Hartree–Fock–Slater calculations on these molecules.
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32.80.Fb Photoionization of atoms and ions
33.60.+q Photoelectron spectra
28.41.Bm Fuel elements, preparation, reloading, and reprocessing

Fourier transform linewidths measurements in NH3 in the vibrational ground state

H. Aroui, A. Picard‐Bersellini, M. Broquier, S. Blanchard, and G. D. Billing

J. Chem. Phys. 89, 5373 (1988); http://dx.doi.org/10.1063/1.455588 (4 pages) | Cited 7 times

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We have measured linewidths of several pure rotational transitions in the vibrational ground state in the far infrared (80–200 cm−1 ). The experiments were conducted by using a Fourier transform spectrometer and gases (NH3 diluted by H2 or He) contained in a 15 cm absorption cell at room temperature. The aim of our study is to discuss the vibrational effect by comparing our measurements with those done in the infrared, 3 and 6 μm regions (ν3 and ν4 bands) and to find evidence for vibrational dependence. The measured pressure broadening cross sections were typically found to be 26 Å2 for the NH3 –H2 collisions and 16 Å2 for the NH3 –He collisions, by comparing these values with those obtained for the ν4 mode, 35 Å2 for the H2 perturber and 17 Å2 for the He perturber, we see a vibrational effect for the NH3 –H2 collisions but not significant for the NH3 –He ones. Our measurements are in good agreement with the theoretical calculations done by Billing by using the semiclassical coupled states method.
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33.20.Ea Infrared spectra
33.70.Jg Line and band widths, shapes, and shifts

Site‐selective excitation of Eu3+ substituted sodium β″ alumina single crystals

A. P. Brown and D. J. Simkin

J. Chem. Phys. 89, 5377 (1988); http://dx.doi.org/10.1063/1.455734 (5 pages) | Cited 5 times

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Broad band excitation spectra of Eu3+ substituted sodium β″ alumina reveals that the Eu3+ ions occupy at least two distinct sites. Examination of the fluorescence spectrum excited by an ultraviolet laser (308 nm) reveals the presence of an additional site. 5D0→7FJ emission spectra characteristic of each site were obtained using site‐selective excitation. A crystal‐field analysis of the emission spectra thus obtained permits the assignment of these sites. The two inhomogeneously broadened 5D0→7F0 emissions at 569.4 and 576.7 nm are assigned as mid oxygen sites perturbed by various arrangements of the residual sodium ions, while the sharp 5D0→7F0 emission at 578.7 nm is assigned as the Beevers–Ross site.
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78.55.Hx Other solid inorganic materials
78.30.-j Infrared and Raman spectra
78.40.-q Absorption and reflection spectra: visible and ultraviolet
71.70.Ch Crystal and ligand fields
66.30.H- Self-diffusion and ionic conduction in nonmetals

Spin relaxation of I>1 nuclei in anisotropic systems. I. Two‐dimensional quadrupolar echo Fourier spectroscopy

István Furó, Bertil Halle, and Tuck C. Wong

J. Chem. Phys. 89, 5382 (1988); http://dx.doi.org/10.1063/1.455589 (16 pages) | Cited 20 times

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The response, in the frequency domain, of half‐integral spin I>1 nuclei in anisotropic systems to the quadrupolar echo (QE) pulse sequence (π/2)x−τ−(π/2)y is investigated, with particular emphasis on the effects of quadrupolar relaxation. Using a state multipole formalism, we derive the frequency spectra produced by one‐ or two‐dimensional Fourier transformation. Powder samples as well as uniformly and partially oriented samples are considered. The 2D QE experiment produces, in the F1 dimension (Fourier transformation with respect to τ), spectra which provide information about the static quadrupole coupling even if only the central line in the QE spectrum (obtained by Fourier transformation of the induction signal after the echo) is detected. For partially oriented and (incompletely dephased) powder samples, the F1 spectra allow the motional spectral densities to be determined with little or no effect of the inhomogeneous quadrupole coupling, which severely complicates the analysis of conventional (single‐pulse) and QE spectra. For completely dephased powder samples (large splittings), the last of the multiple spin echoes gives rise to a triplet QE spectrum (for any I≥3/2), the satellite decay in which yields a transverse relaxation rate.
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76.60.Gv Quadrupole resonance
76.60.Es Relaxation effects
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Study on YAG:Nd3+ spectra. I. Absorption spectra

Dao‐hong Hua, Zeng‐fu Song, Shu‐kun Wang, and Zu‐xiu Rong

J. Chem. Phys. 89, 5398 (1988); http://dx.doi.org/10.1063/1.455590 (6 pages) | Cited 9 times

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Absorption spectra of YAG:Nd3+ in the region 28 000–39 500 cm−1 at liquid helium temperature (LHeT) and liquid nitrogen temperature (LNT) have been studied. The whole absorption spectra of YAG:Nd3+ at room temperature (RT) has been measured. Based upon the present and earlier measurements the data at three temperatures are listed. By using the irreducible tensor method, we diagonalized the parametrized D2 Hamiltonian in a free‐ion wave function space involving the whole J multiplets, fitting the eigenvalues to the experiment data at LNT, we assigned the whole Stark levels by using the eigenvectors obtained.
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42.55.Rz Doped-insulator lasers and other solid state lasers
78.40.Ha Other nonmetallic inorganics
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.70.Ch Crystal and ligand fields

Study on YAG:Nd3+ spectra. II. Fluorescence spectra

Zeng‐fu Song, Dao‐hong Hua, Shu‐kun Wang, and You‐xi Gui

J. Chem. Phys. 89, 5404 (1988); http://dx.doi.org/10.1063/1.455591 (4 pages) | Cited 1 time

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Several fluorescence line groups in the infrared, visible, and ultraviolet regions are observed by exciting YAG:Nd3+ crystal with Ar+ laser (5145 Å) and x‐ray at liquid nitrogen temperature (LNT) and room temperature (RT), respectively. All of these line groups are assigned properly. Some new Stark levels are determined from the fluorescence spectra. The excited state absorption process is observed.
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42.55.Rz Doped-insulator lasers and other solid state lasers
78.55.Hx Other solid inorganic materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

The structure of the nitrous oxide dimer from sub‐Doppler resolution infrared spectroscopy

Z. S. Huang and R. E. Miller

J. Chem. Phys. 89, 5408 (1988); http://dx.doi.org/10.1063/1.455592 (9 pages) | Cited 48 times

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The opto‐thermal detection method has been used to obtain rotationally resolved infrared spectra for both (14N14N16O)2 and (15N14N16O)2. The vibrational band observed in each case correlates with the ν1+ν3 band of the N2O monomer. A large number of A‐ and B‐type transitions have been assigned and fit for both species yielding accurate molecular constants for both the ground and excited vibrational states. From intensity alternations associated with nuclear spin statistics and the small inertia defect [Δ″=0.611 amu Å2 for (14N14N16O)2], it is clear that the nitrous oxide dimer has a slipped parallel geometry which possesses a center of symmetry. Isotopic substitution shows that of the two such structures, only the one having the oxygen atoms close to one another is experimentally observed. The structural constants are determined to be RNN=3.493(4) Å and θNNO=59.2(5)°.
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33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
36.40.-c Atomic and molecular clusters

Effect of pressure on the internal rotation angle of biphenyl in carbon disulfide

Minoru Katō, Mikio Higashi, and Yoshihiro Taniguchi

J. Chem. Phys. 89, 5417 (1988); http://dx.doi.org/10.1063/1.455593 (5 pages) | Cited 12 times

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The effect of pressure on the conformation of biphenyl in carbon disulfide was measured by using high pressure infrared spectroscopy with a diamond anvil up to 13 kbar. Pressure effects on the nonplanar vibrational modes indicate that the dihedral angle decreases at the rate of 2° kbar−1. Under high pressure the frequency of the C–H stretching vibrational modes shifts to blue so that the repulsive force becomes more predominant in the solute–solvent interactions between CH and CS2 molecule. The decrease in the dihedral angle of biphenyl induced by compression is related to the change of the intrinsic volume of the biphenyl molecule.
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33.20.Ea Infrared spectra
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

The 2 1Ag state in the linear polyene 2,4,6,8,10,12,14,16‐octadecaoctaene

Bryan E. Kohler, Charles Spangler, and Curtis Westerfield

J. Chem. Phys. 89, 5422 (1988); http://dx.doi.org/10.1063/1.455594 (7 pages) | Cited 69 times

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High resolution fluorescence and fluorescence excitation spectra have been obtained for the all‐trans polyene 2,4,6,8,10,12,14,16‐octadecaoctaene in an n‐hexadecane matrix at 4.2 K. This is the longest discrete linear polyene for which such data are known. The 1 1Ag to 2 1Ag 0–0 band at 17 871 cm−1 is 4900 cm−1 below 1 1Ag to 1 1Bu 0–0 band at 22 770 cm−1. Both of these excitation energies are approximately what would have been predicted by fitting the 0–0 excitation energies of shorter polyenes with N double bonds by a 1/N curve and extrapolating to N=8. These spectra provide further information on the vibronic levels of the ground (1 1Ag) and first excited (2 1Ag ) singlet states and provide insight into the structure of the conjugated polymer polyacetylene. As has been found in the case of shorter polyenes, the strongest vibronic feature (assigned as a totally symmetric C=C stretch) increases 1554 cm−1 in the 1 1Ag state to 1799 cm−1 in the 2 1Ag state) also for the octaene. Possible reasons for this increase are discussed.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Lg Ultraviolet spectra
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Two‐photon (vacuum ultraviolet + visible) spectroscopy of argon, krypton, xenon, and molecular hydrogen

M. P. McCann, C. H. Chen, and M. G. Payne

J. Chem. Phys. 89, 5429 (1988); http://dx.doi.org/10.1063/1.455595 (13 pages) | Cited 13 times

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Two‐photon transitions have been examined in argon, krypton, xenon, and molecular hydrogen using a coherent vacuum ultraviolet (VUV) photon at a fixed wavelength of 118 nm and a tunable photon from a dye laser. The 118 nm VUV photon is produced by third harmonic generation in xenon using UV light at 355 nm from a frequency tripled Nd:YAG laser. Though the VUV intensity is very weak, (∼100 nJ per pulse) it was utilized very efficiently since most of VUV photons in the ionization region were absorbed. Spectra were obtained in the region of 12.5 to 13.5 eV and the corresponding two‐photon rate constants were calculated. This is the first time that coherent VUV light has been employed with tunable visible light for the production of two‐photon spectra and the measurement of two‐photon rates. The two‐photon ionization rate of xenon was measured using photons at fixed wavelengths of 118 and 355 nm. A new parameter is proposed for direct comparison of the data from various two‐photon experiments.
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32.80.Wr Other multiphoton processes
33.80.Wz Other multiphoton processes
32.80.Rm Multiphoton ionization and excitation to highly excited states

Photoelectron spectroscopy of the halocarbene anions HCF−, HCCl−, HCBr−, HCI−, CF−2, and CCl−2

Kermit K. Murray, Doreen G. Leopold, Thomas M. Miller, and W. C. Lineberger

J. Chem. Phys. 89, 5442 (1988); http://dx.doi.org/10.1063/1.455596 (12 pages) | Cited 60 times

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The 488 nm photoelectron spectra are reported for the HCX(math1A′)+e−←HCX−(math2A″) and HCX(math3A″)+e−←HCX−(math2A″) transitions in HCF−, DCF−, HCCl−, HCBr−, and HCI− and for the CX2(math1A1)+e−←CX−2(math2B1) transitions in CF−2 and CCl−2 . Adiabatic electron affinities are found to be 0.557±0.005 eV (HCF), 0.552±0.005 eV (DCF), 1.213±0.005 eV (HCCl), 1.556±0.008 eV (HCBr), 1.683±0.012 eV (HCI), 0.179±0.005 eV (CF2), and 1.603 ± 0.008 eV (CCl2). Bounds for the triplet excitation energies are determined for all the halocarbenes for which photoelectron spectra were observed, with the exception of CCl2. For the HCX halocarbenes, upper bounds for the triplet excitation energies are 14.7±0.2 kcal/mol (HCF, DCF), 11.4±0.3 kcal/mol (HCCl), and 9±2 kcal/mol (HCBr). A more detailed analysis of HCF suggests the actual triplet excitation energy to be 11.4±0.3 kcal/mol, 14.7±0.2 kcal/mol, or 8.1±0.4 kcal/mol, with the first value the most likely. Since the multiplicity of the ground state of HCl is not known, we report the energy of its first excited state to be less than 9±2 kcal/mol. The absence of an observed triplet state in the CF−2 photoelectron spectrum allows us to assign a lower bound on the triplet excitation energy of CF2 of 50 ± 2 kcal/mol.
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33.60.+q Photoelectron spectra
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

The microwave spectrum of SiF+

Rudolph H. Petrmichl, Kirk A. Peterson, and R. Claude Woods

J. Chem. Phys. 89, 5454 (1988); http://dx.doi.org/10.1063/1.455597 (6 pages) | Cited 22 times

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The first detection of the silicon monofluoride cation by spectroscopic means has been achieved at millimeter and submillimeter wavelengths. Frequencies of rotational transitions spanning a range of J values from 1 to 14 and all vibrational states from v=0 to 15 were precisely measured. Lines of 29 SiF+ up to v=4 and 30 SiF+ up to v=3 were also included in this study. These data were all well fit by a standard Dunham expansion with eight terms, with no requirement for a Watson type ΔSi01 parameter, describing breakdown of the Born–Oppenheimer approximation, to explain the isotope dependence. The parameters Be (or re ), ωe , and the Dunham potential constants a1 –a5 were well determined from this analysis and showed very satisfying agreement with the results of our recent large basis set MP4SDQ and CI calculations, which we had used to determine the search range for locating the spectrum of SiF+ . The final results are re =1.526 495 0(2) Å and ωe =1050.7(2) cm−1.
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33.20.Bx Radio-frequency and microwave spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Dj Interatomic distances and angles
33.20.Sn Rotational analysis

Autoionizing Rydberg states of Li2: Analysis of electronic–rotational interactions

M. Schwarz, R. Duchowicz, W. Demtröder, and Ch. Jungen

J. Chem. Phys. 89, 5460 (1988); http://dx.doi.org/10.1063/1.455598 (13 pages) | Cited 23 times

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Highly excited Rydberg states of 7Li2 have been measured by two‐step excitation with two narrow band pulsed dye lasers in a collimated lithium beam. A complex many‐line two‐photon ionization spectrum has been observed which consists of sharp lines whose natural widths are smaller than the laser line width (0.03 cm−1). The spectrum has been analyzed with the help of multichannel quantum defect theory. Radial electronic dipole transition moments for the second excitation step were calculated and provided the key to the analysis. The spectra correspond to the excitation of s and d Rydberg series with n∼18–40. The series are affected by strong rotational l uncoupling as well as electronic s–d mixing. The analysis yields accurate values for the vibrational and rotational constants for the X 2Σ+g state of Li+2 and an improved value of the ionization potential of Li2.
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36.40.-c Atomic and molecular clusters
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Mt Rotation, vibration, and vibration-rotation constants

Rotationless molecular vibrations

E. J. Shipsey

J. Chem. Phys. 89, 5473 (1988); http://dx.doi.org/10.1063/1.455599 (13 pages) | Cited 3 times

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Relative coordinates convenient for variational calculations are discussed. The coordinates, for suitable representations of the potential, allow matrix elements to be expressed as sums of products of one‐dimensional integrals for product basis functions. A small vibration limit is reviewed in these coordinates. Examples are given for application to the linear triatomic, water, ammonia, acetylene, and finally methane.
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33.20.Tp Vibrational analysis

A variational calculation of the molecular vibrations of H2O for states with zero angular momentum

E. J. Shipsey and D. A. Kohl

J. Chem. Phys. 89, 5486 (1988); http://dx.doi.org/10.1063/1.455600 (6 pages) | Cited 3 times

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A different approach for calculating the zero angular momentum, vibrational energy levels of polyatomic molecules was implemented for H2O. The special features of this approach are that, even for arbitrarily large amplitudes of vibration, all operators in the Hamiltonian are easily evaluated analytically, there are no pathological singularities, angular momentum is rigorously decoupled, and the variables are a mixture of two curvilinear and 3N−8 Cartesian coordinates. As a demonstration of the approach, a full variational calculation was done and the results are compared with a prior result based on the Watson Hamiltonian. Although the two Hamiltonians appear to be very different and although two different computational methods were employed, the results of the two independent calculations were virtually identical for the lowest 14 vibrational states of H2O. Compared to the conventional normal coordinate formalism, the kinetic energy operator contains products of anti‐Hermitian operators and these ‘‘extra’’ terms are found to change the vibrational frequencies by tens of wave numbers.
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33.20.Tp Vibrational analysis

Understanding dephasing in mixed molecular crystals. I. Photon echoes from dimers revisited

Frank C. Spano and W. S. Warren

J. Chem. Phys. 89, 5492 (1988); http://dx.doi.org/10.1063/1.455601 (6 pages) | Cited 4 times

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We show that a fundamental assumption used in analyzing photon echo decays from interacting molecules—the assumption that the ‘‘pure’’ dephasing rate can be obtained by subtracting one half of the fluorescence decay rate (2T1)−1 from the photon echo decay rate—is generally inconsistent with a fully quantum mechanical treatment. The density matrix evolution for a system of noninteracting dimers is calculated using the retarded electromagnetic coupling between two oscillating dipoles. We are able to properly include the effects of spontaneous emission and Dicke superradiance on the echo decay.
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78.55.Kz Solid organic materials
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Visible and ultraviolet resonance enhance multiphoton ionization photoelectron spectroscopy of H2S in the one‐photon wavelength region 143–158 nm

Jhobe Steadman, S. Keith Cole, and Tomas Baer

J. Chem. Phys. 89, 5498 (1988); http://dx.doi.org/10.1063/1.455602 (9 pages) | Cited 8 times

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The Rydberg states of H2S have been investigated by multiphoton ionization, resonant enhanced at the two‐photon and three‐photon level (REMPI). The REMPI spectra (ion signal vs laser wavelength) are compared to the one‐photon absorption spectrum. In addition, photoelectron spectra (PES) were collected at most of the absorption peaks in both the 2+1 and 3+1 REMPI processes. The vibrational state distribution of H2S+ formed by REMPI at a number of laser wavelengths is highly peaked at a single vibrational level. These intermediate Rydberg states could therefore be assigned on the basis of the PES. The REMPI‐PES at other laser wavelengths were more complex probably because of perturbed intermediate Rydberg states. A comparison of the 2+1 and 3+1 REMPI wavelength scans shows significant peak intensity differences, which we attribute to the different Δl selection rules in the two‐ and three‐photon absorption steps. New H2S 4p Rydberg states were observed in the two‐photon resonance study, and a number of previously observed peaks have been reassigned on the basis of these results.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.60.+q Photoelectron spectra

The production and spectroscopy of excited sulfur atoms from the two‐photon dissociation of H2S

Jhobe Steadman and Tomas Baer

J. Chem. Phys. 89, 5507 (1988); http://dx.doi.org/10.1063/1.455603 (7 pages) | Cited 15 times

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Ground (3PJ) and excited state (1D2, 1S0) sulfur atoms have been produced by the two‐photon photodissociation of H2S in the wavelength range 285–316 nm. The resultant sulfur atoms undergo 2+1 resonance enhanced multiphoton ionization (REMPI) at selected laser wavelengths. The initial and final ion states in the 2+1 REMPI process have been determined through the analyses of the REMPI spectrum (laser wavelength scan) and the REMPI‐PES taken at the atomic resonances. The intermediate states accessed in the two‐photon excitations have been assigned. Several transitions which originate from the 1S0 excited state of atomic sulfur have been observed. The intermediate states of these transitions lie above the ionization continuum and are depleted competitively by autoionization and further photon absorption. Extremely pure state selection of ground and excited sulfur atomic ions is demonstrated at several of the two‐photon resonances. Evidence of configuration interaction between the 6p 3P1, 6p 5P1, and 4p 1P1 levels is presented.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.60.+q Photoelectron spectra

Optical spectra of Yb atoms and dimers in rare gas matrices

Sefik Suzer and Lester Andrews

J. Chem. Phys. 89, 5514 (1988); http://dx.doi.org/10.1063/1.455576 (3 pages) | Cited 3 times

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Matrix isolated Yb vapor spectra show absorptions due to atoms, dimers, and higher aggregates. The atomic spectrum reveals strong 395 and 344 nm bands and very sharp weaker 267 and 255 nm absorptions in solid argon. The spectrum of Yb2 shows extensive vibrational stucture around 550 nm both in Ar and Kr matrices with a spacing of 48 cm−1. This absorption is assigned to a 6s2(1S0)6s2(1S0)(1Σ+g) →6s2(1S0)6s6p(1P1)(1Σ+u) transition similar to the one observed for group IIA metal dimers. Higher aggregate spectra overlap with the 550 nm dimer and weak atomic band.
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32.30.Jc Visible and ultraviolet spectra
36.40.-c Atomic and molecular clusters
33.20.Lg Ultraviolet spectra

Resonant two‐photon ionization spectroscopy of jet‐cooled Pt2

Scott Taylor, George W. Lemire, Yoon Mi Hamrick, Zhenwen Fu, and Michael D. Morse

J. Chem. Phys. 89, 5517 (1988); http://dx.doi.org/10.1063/1.455577 (7 pages) | Cited 72 times

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The gas phase optical spectrum of jet‐cooled Pt2 has been investigated over the range of 11 300 to 26 300 cm−1 using resonant two‐photon ionization spectroscopy in combination with time‐of‐flight mass spectrometry. Numerous vibronic bands are observed. Analysis of the data gives the location of some 26 excited electronic states, which are characterized by the frequencies of their origin bands, vibrational frequencies, and anharmonicities. Variation of the second color in a two‐color resonant two‐photon ionization scheme has determined the ionization threshold of Pt2 to be 8.68±0.02 eV. The observation of the onset of predissociation, characterized by a sharp drop in excited state lifetime, places the dissociation energy of Pt2 at 3.14±0.02 eV. In combination with the Pt atomic ionization potential of 8.8±0.2 eV, these results give the bond strength of Pt+2 as D0(Pt−Pt+)=3.26±0.24 eV. The strength of the chemical bond in Pt2, as compared to Au2, demonstrates that there are significant 5d contributions to the chemical bonding in Pt2.
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36.40.-c Atomic and molecular clusters
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.15.Ta Mass spectra
33.15.Fm Bond strengths, dissociation energies

Fluorescence cross section of the H2O+ math 2A1 (0, 7, 0) produced through photoionization of H2O

C. Y. Robert Wu and M. Y. Hwang

J. Chem. Phys. 89, 5524 (1988); http://dx.doi.org/10.1063/1.455558 (3 pages) | Cited 2 times

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The cross section for production of the H2O+ math 2A1(0,7,0)→math 2B1(0,0,0) fluorescence through photoionization of H2O has been measured in the 14.5–20.5 eV region. The maximum quantum yield is 1.4×10−3 at 16.5 eV. Further, the cross sections for producing the H2O+[math 2A1(0,7,0)] and H2O+ math 2A1 have been estimated. The magnitude of the latter is about a factor of 10 smaller than that obtained by electron spectroscopy. The discrepancy can be attributed to radiationless transitions between the math and math states of H2O+.
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33.50.Dq Fluorescence and phosphorescence spectra
33.80.Eh Autoionization, photoionization, and photodetachment
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Multiphoton ionization photoelectron spectroscopy study of OCS: Rydberg vibronic structure and ion state selection

Baorui Yang, Mohamad H. Eslami, and Scott L. Anderson

J. Chem. Phys. 89, 5527 (1988); http://dx.doi.org/10.1063/1.455559 (8 pages) | Cited 23 times

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Multiphoton ionization (MPI) in conjunction with photoelectron spectroscopy (PES) has been used to examine Rydberg states of OCS in the energy range from 70 547 to 75 472 cm−1. The combination of techniques allows us to correct previous assignments for several vibronic bands, and to probe vibronic mixing in the Rydberg levels. In the course of this study we have found routes for preparing OCS+ with control over both vibrational mode and fine structure state.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.60.+q Photoelectron spectra
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

A systematic study of polarizability and microscopic third‐order optical nonlinearity in thiophene oligomers

Ming‐Tang Zhao, Bhanu P. Singh, and Paras N. Prasad

J. Chem. Phys. 89, 5535 (1988); http://dx.doi.org/10.1063/1.455560 (7 pages) | Cited 125 times

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A systematic study of the dependence of the band gap, the linear optical susceptibility, the polarizability α, and the second hyperpolarizability γ, on the number of repeat unit is conducted for the thiophene series from monomer to hexamer. The linear optical susceptibilities for oligomers have been determined from the refractive index measurements on vacuum deposited films using the m lines technique. The orientationally averaged polarizabilities 〈α〉 have been measured from refractive index measurements of THF solutions. The orientationally averaged second hyperpolarizabilities 〈γ〉 have been measured by degenerate four‐wave mixing studies of THF solutions. The validity of the Lorentz–Lorenz approximation is tested and found to be satisfactory. The experimental values of 〈α〉 and 〈γ〉 for thiophene and 〈α〉 for bithiophene are found to be in qualitative agreement with those obtained by a recent ab initio calculation which used the finite field method and included diffuse polarization functions. The experimentally observed dependence of 〈α〉 and 〈γ〉 on the number N of the thiophene repeat unit is compared with that predicted by a free electron model, PPP methods, and the ab initio calculations. For the case of polarizability, the repeat unit dependence is in good agreement with that predicted by the ab initio calculations but for the case of second hyperpolarizability, the agreement is not as good.
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36.20.Kd Electronic structure and spectra
42.65.-k Nonlinear optics
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

The effect of transverse cross relaxation on nuclear magnetic resonance dipolar spectra

Zhe‐Hong Gan, Julio C. Facelli, and David M. Grant

J. Chem. Phys. 89, 5542 (1988); http://dx.doi.org/10.1063/1.455698 (5 pages) | Cited 5 times

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The 13C dipolar powder spectra of 13CH3 31PO(OH)2 at room temperature and 13CH3 19F at low temperature (T=25 K) are reported. An intense peak is observed at the center of the Pake doublet. This phenomenon is explained by the transverse cross relaxation mechanism between the 13C and either the 31P or 19F nuclei. This theory shows the importance of the nonsecular terms in the Redfield relaxation theory. The chemical shielding tensors and dipolar coupling constants of these two molecules are obtained by fitting the experimental spectra.
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76.60.Es Relaxation effects
33.25.+k Nuclear resonance and relaxation

Slow manifolds and mixed‐mode oscillations in the Belousov–Zhabotinskii reaction

Dwight Barkley

J. Chem. Phys. 89, 5547 (1988); http://dx.doi.org/10.1063/1.455561 (13 pages) | Cited 21 times

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The mixed‐mode oscillations observed at high flow rates in the Belousov–Zhabotinskii (BZ) reaction are considered and comparison is made between these oscillations and the dynamics of three different mathematical models based on slow manifolds. It is shown that the model proposed by Rössler for the generation of complex behavior in nonequilibrium chemical reactions is in conflict with the behavior of the BZ reaction. It is also shown that a slow‐manifold model based on the hysteresis‐Hopf normal form fails to accurately reproduce the oscillations found at high flow rates in the BZ system. A model of the type first proposed by Boissonade is presented; the model consists of the coupling of two simple systems. It is shown that this model naturally generates mixed‐mode oscillations like those observed in the BZ reaction.
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82.40.Bj Oscillations, chaos, and bifurcations
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