Isao H. Suzuki

Monochromator for a soft X-ray photochemistry beamline BL27SU of SPring-8

A high-resolution monochromator with varied line space plane gratings (VLSG) and spherical focusing mirrors was installed in one of three branches of BL27SU in SPring-8. The performance of the monochromator was roughly evaluated from the photo ion yield of nitrogen molecule. Furthermore, the kinetic energy of the photoelectron from Xe 5p3/2 orbit was also measured at the same photon energy with the N2 to avoid the influence of natural width. The resolving power over 104 has been confirmed at the N K-edge.

Multiple photoionization in Ne, Ar, Kr and Xe from 44 to 1300 eV

Abstract Yields of multiply charged ions produced from photoabsorption of Ne, Ar, Kr and Xe over the photon energy range 44–1300 eV have been measured using a time-of-flight mass spectrometer and monochromatized synchrotron radiation. The ion yields were converted into partial photoionization cross-sections using the total photoionization cross-sections reported in the literature. These partial photoionization cross-sections show the relative importance of shake-up or shake-off processes in the initial photoabsorption step and the subsequent Auger transitions in the production of multiply charged ions.

Kinetic energy release from N2 induced by selective inner-shell excitation

Abstract Dissociative ionization of N2 which has absorbed soft X-rays has been studied by means of a time-of-flight (TOF) mass spectrometric technique. The TOF spectra resulting from the inner-shell excited state and the inner-shell ionized state of N2 are found to be different from each other. The kinetic energy distributions of fragment ions, N+ and N2+, are obtained on the basis of a simulation calculation of the TOF spectra. Fragmentation channels to N+ and N2+ are assigned from these distributions.

Dipole moment functions of carbon dioxide and nitrous oxide

Abstract The vibrational wavefunctions obtained from the direct numerical diagonalization of the vibrational Hamiltonian matrix are used to compute the matrix elements of transition dipole moments for carbon dioxide and nitrous oxide. The computed matrix elements are found very close to those obtained previously by the contact transformation method. The least-squares fit of the dipole moment derivatives up to the second order has been attempted. It is shown that the values as well as the signs of the second derivatives can be determined if the mechanical anharmonicity contributes considerably to the corresponding combination and/or difference bands. The bands selected for N 2 O include the fundamentals, first overtones, binary combination, and difference bands as well as the bands coupled with the above by Fermi resonances. The converged set of the dipole moment derivatives of N 2 O gives the computed matrix elements very close to the observed. This also demonstrates the wider applicability of the direct diagonalization method.

Shake-off Processes in Photoionization and Auger Transition for Rare Gases Irradiated by Soft X-Rays

Branching ratios of multiply charged Ne, Ar, Kr and Xe ions produced following soft X-ray absorption by the rare gases have been measured using a time-of-flight mass spectrometer and monochromatized synchrotron radiation. Ratios of double, triple and quadruple valence photoionization to single valence photoionization, of multiple Auger transitions to the normal Auger transition from a core hole or core-valence two-hole state, and of the multiple photoionization with a core hole to single core photoionization have been determined using the measured branching ratios of the multiply charged ions.

Sextic force field of nitrous oxide

Abstract The sextic force field in the curvilinear internal coordinates has been studied for the nitrous oxide molecule from the spectroscopic data of 14 N 2 16 O, 14 N 15 N 16 O, and 15 N 14 N 16 O. The bands below 6600 cm −1 have been used. The force constants in the internal coordinates are converted to those in dimensionless normal coordinates by two successive transformations. The vibration Hamiltonian matrix for each symmetry species of a given isotopic species has been constructed from the harmonic oscillator basis functions, and it is then diagonalized numerically to give the vibrational energy levels and the wavefunctions. The latter have been used for the evaluation of ratational constants. The least-squares refinement has been very successful in the present study, and it is shown that the general quartic force field supplemented by the quintic and sextic stretching diagonal force constants estimated from the Morse function, provided that the terms up to sextic are kept in the dimensionless normal coordinate space, well reproduces the spectroscopic constants such as the vibrational levels, rotational constants, l -type doubling constants, and centrifugal distortion constants. The spectroscopic constants of the isotopic molecules which are excluded from the refinement process are also in good agreement with the computed ones. The bond dissociation energies of the NN and NO bonds estimated from the present results have been critically examined.

Dipole moment function of carbonyl sulfide from analysis of precise dipole moments and infrared intensities

Precise (±3×10−5 D) dipole moments of OCS in 11 vibrational states (0000, 1000, 2000, 0110, 0200, 0220, 0310, 0400, 1200, 1420, 2200) of the normal species and two states (0000 and 0200) of both OC34S and O13CS derived from our recent LMDR (infrared laser–microwave double resonance with intense electric field) measurements were combined with the previous MBER (molecular beam electric resonance) results for the 0000 and 0110 states of the normal, 34S, 13C, and 18O species and the transition moments for various vibrational bands obtained from infrared intensity measurements, to determine the dipole moment function. Curvilinear coordinates were used to describe the vibrational displacements. The dipole moment vector was represented in terms of the components parallel and perpendicular to the C–O bond. Thus the dipole moments of various isotopic species may be analyzed simultaneously. The dipole moments and the transition moments were calculated as the diagonal and nondiagonal matrix elements of dipole moment...

Asymmetry in the ionic fragmentation of N2O photoexcited around the N and O K edges

Asymmetry parameters (β) for the fragment ions of N2O following excitation or ionization of the N and O K shell electrons have been determined from photoelectron–photoion coincidence (PEPICO) and photoion–photoion coincidence (PIPICO) spectra measured using monochromatized synchrotron radiation and a rotatable time‐of‐flight mass spectrometer. Profiles of the β parameters from the N+ ions with low kinetic energies (K.E. <4.5 eV) in the PEPICO spectra were found to be very isotropic (close to 0) around both the N and O K edges. β parameter profiles for the O+ ions with contributions from N+ ions with K.E. ≳4.5 eV and N2+ ions overlapped with NO+ ions show structure with negative values at the π* resonances below the N K‐edges and positive values at the unresolved Rydberg resonances below the terminal N K edge and O K edge and at the shape resonance above the N K edges. β parameters from the N+–NO+ and N2+–O+ PIPICO signals were found to be considerably more anisotropic than the corresponding values from th...

Carbon K-shell photoelectron angular distribution from fixed-in-space CO2 molecules

Measurements of photoelectron angular distributions for carbon K-shell ionization of fixed-in-space CO2 molecules with the molecular axis oriented along, perpendicular and at 45 degrees to the electric vector of the light are reported. The major features of these measured spectra are fairly well reproduced by calculations employing a relaxed-core Hartree-Fock approach. In contrast to the angular distribution for K-shell ionization of N-2, which exhibits a rich structure dominated by the f-wave (l = 3) at the shape resonance, the angular distribution for carbon K-shell photoionization of CO2 is quite unstructured over the entire observed range across the shape resonance.

Site-specific fragmentation caused by core-level photoionization in F3SiCH2CH2Si(CH3)3 vapor: Comparison between Si:1s and 2p photoionizations by means of photoelectron-photoion-photoion triple-coincidence spectroscopy

Site-specific fragmentation caused by Si:1s and 2p core-level photoionizations in F(3)SiCH(2)CH(2)Si(CH(3))(3) vapor was studied by energy-selected-photoelectron photoion-photoion triple-coincidence spectroscopy. The difference between the chemical shifts of the two Si sites is larger for the 1s ionization than for the 2p (2s) ionization. The fragmentation caused by the Si:1s ionization is more violent than that caused by the Si:2p ionization. The ions and ion pairs showing high site specificity for the Si:1s ionization belong to small fragments compared to those in the Si:2p ionization. Criteria for high site-specificity in fragmentation are discussed in conjunction with the present results.