Jun-ichi Adachi - Academia.edu (original) (raw)
Papers by Jun-ichi Adachi
Photoelectron–photoion–photoion momentum spectroscopy as a direct probe of the core-hole localization in C 1s photoionization of C2H2
Journal of Physics B: Atomic, Molecular and Optical Physics, 2007
ABSTRACT Angular distributions of C 1s photoelectrons, relative to a dissociation axis for C2H2, ... more ABSTRACT Angular distributions of C 1s photoelectrons, relative to a dissociation axis for C2H2, have been measured with a photoelectron–photoion–photoion coincidence technique. The photoelectron angular distribution (PAD) for three two-body fragmentations (symmetric, non-symmetric and proton-migration fragmentations) is completely different. The PADs for non-symmetric fragmentation provide direct evidence of a localized core-hole and preferential bond breaking following Auger decays. Moreover, the PAD for symmetric fragmentation has been interpreted as the interference between photoemissions from the two carbon atoms.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2011
Three-photon double ionization of an Ar atom has been investigated by photoelectron spectroscopy ... more Three-photon double ionization of an Ar atom has been investigated by photoelectron spectroscopy using an extreme ultraviolet free-electron laser. When the photon energy of the laser has been tuned to the resonances of the intermediate Ar + ion, photoelectron peaks due to the resonant two-photon single ionization of the Ar + ion have been observed. And it has been revealed that the appearance of the peaks is controlled by the mixing ratios of 3p 4 core-configurations of the multi-configuration states. Furthermore, it has been shown that the laser intensity dependence of the Ar 2+ ion production rate due to the resonant two-photon single ionization strongly deviates from that expected by perturbation theory.
The Journal of Chemical Physics
Operando time-resolved soft x-ray absorption spectroscopy (TR-SXAS) is an effective method to rev... more Operando time-resolved soft x-ray absorption spectroscopy (TR-SXAS) is an effective method to reveal the photochemical processes of metal complexes in solutions. In this study, we have developed the TR-SXAS measurement system for observing various photochemical reactions in solutions by the combination of laser pump pulses with soft x-ray probe pulses from the synchrotron radiation. For the evaluation of the developed TR-SXAS system, we have measured nitrogen K-edge x-ray absorption spectroscopy (XAS) spectra of aqueous iron phenanthroline solutions during a photoinduced spin transition process. The decay process of the high spin state to the low spin state in the iron complex has been obtained from the ligand side by N K-edge XAS, and the time constant is close to that obtained from the central metal side by time-resolved Fe K-edge XAS in the previous studies.
The Journal of Physical Chemistry, 1996
Fragment ion yields in the C 1s f Rydberg excitation region of CO 2 were measured in the 90°and 0... more Fragment ion yields in the C 1s f Rydberg excitation region of CO 2 were measured in the 90°and 0°d irections relative to the electric vector of the linearly polarized light. The C 1s f ns (n) 3, 4), npπ and npσ (n) 3-7), and nd (n) 3, 4) Rydberg transitions are clearly observed and show some vibrational structures. The dipole-forbidden C 1s(σ g) f 3sσ g Rydberg transition is the strongest of all the Rydberg transitions, and the ion yield in the 90°direction is dominant. This indicates that the bending vibration is predominantly coupled with the 3sσ g Rydberg state and the intensity-lending dipole-allowed state is a very strong π* resonance, only 2 eV lower than the 3sσ g state. On the other hand, in the 4sσ g Rydberg state the vibronic coupling through the antisymmetric stretching mode is strongly observed in the 0°direction. This is probably because the 4sσ g state approaches another intensity-lending state with Σ u + symmetry and goes away from the π* resonance. The angle-resolved ion-yield technique is very powerful for elucidating the vibronic coupling mechanism.
Angle Resolved Photoion Spectroscopy of Core-Excited Free-Molecules
Fixed-Molecule 1sσg,u Photoelectron Angular Distributions as a Probe of σg* and σu* Shape Resonances of CO2
Physical Review Letters, 1997
ABSTRACT
Physical Review Letters, 1995
The angular distributions of 1sophotoelectrons from N2 molecules held fixed in space have been me... more The angular distributions of 1sophotoelectrons from N2 molecules held fixed in space have been measured around the or* shape resonance for the first time, The angular distributions have been very rich in structure, which are completely different from usual photoelectron angular distributions from randomly oriented molecules, as predicted by Dill. The orbital angular momentum properties of the 1scr photoelectrons around the o. * shape resonance have been made clear from the angular distribution patterns.
Angular Correlation Between B K-VV Auger Electrons of BF3 Molecules and Coincident Fragment Ions: Manifestation of the Difference Between the Angular Correlation and Molecular Frame Auger Electron...
Physical Review Letters, 2013
We have measured the angular correlation between the B K-VV Auger electrons of BF(3) molecules an... more We have measured the angular correlation between the B K-VV Auger electrons of BF(3) molecules and the coincident fragment-ion pairs of BF(2)(+)-F(+). Then, we have found that the measured angular correlation patterns depending on the mutual angle between the light polarization direction and molecular orientation are affected by the anisotropic axis distribution of the molecular ensemble of BF(3)(+) reflecting the anisotropic nature of photon-molecule interaction. In this context, we have pointed out generally that for coincidence experiments, so-called molecular frame Auger electron angular distributions are realized only if the axis distribution of the molecular ion ensemble is isotropic.
Shape-Resonance-Enhanced Vibrational Effects in the Angular Distributions of C 1s Photoelectrons from Fixed-in-Space CO Molecules
Physical Review Letters, 2003
Angular distributions of C 1s photoelectrons from fixed-in-space CO molecules have been measured ... more Angular distributions of C 1s photoelectrons from fixed-in-space CO molecules have been measured with vibrational resolution. A strong dependence of the angular distributions on the vibrational states of the residual molecular ion has been found for the first time in the region of the shape resonance. Calculations in the relaxed core Hartree-Fock approximation have reproduced the angular distributions fairly well in the general shapes of the angular distributions due to the correct description of nuclear motion as an average of the internuclear-distance-dependent dipole amplitudes.
Direct Probe of the Shape Resonance Mechanism in 2σg-Shell Photoionization of the N2 Molecule
Physical Review Letters, 2002
ABSTRACT
Photoelectron Angular Distributions from O K Shell of Oriented CO Molecules: A Critical Comparison between Theory and Experiment
Physical Review Letters, 2000
The dynamical information (ten dipole matrix elements and eight phase differences) has been deduc... more The dynamical information (ten dipole matrix elements and eight phase differences) has been deduced from the measured angular distributions of photoelectrons from O K shell of oriented CO molecules near the ionization threshold in the region of a sigma(*) shape resonance. Light polarization parallel and perpendicular to the molecular axis has been used. An important contribution of six lsigma partial waves with 0</=l</=5 to the sigma(*) shape resonance is demonstrated. A comparison with our calculations in the relaxed core Hartree-Fock approximation reveals only a qualitative agreement, therefore a more advanced theory is needed.
Direct Determination of Partial Wave Contributions in the σ* Shape Resonance of CO Molecules
Physical Review Letters, 1998
ABSTRACT
Physical Review A, 2011
The two-photon resonance ionization probability of atoms in strong extreme-ultraviolet free-elect... more The two-photon resonance ionization probability of atoms in strong extreme-ultraviolet free-electron laser (EUV FEL) pulses has been investigated by the model of time-dependent wave packet propagation of a lightcoupled multilevel atom. Under the simulation within the model assuming single-mode FEL pulses, the ionization probability P ion has shown characteristic dependences on the scaled coupling parameter U gi between two levels of the ground (g) and intermediate (i) resonance states, namely, P ion ∝ (U gi) n , with n being equal to ∼2, less than 1, and ∼1 for the small, medium, and large U gi regimes, respectively. This power dependence of the ionization probability has been interpreted due to Rabi oscillations between g and i states. To compare with recent experimental results on the same condition, the multimode nature of self-amplitude spontaneous emission (SASE) FEL pulses has been managed in the simulation. Then, the recent experimental laser-power dependence of the two-photon resonance ionization of He [Sato et al., J. Phys. B 44, 161001 (2011)] has been well described by that for the large U gi regime of the simulation, i.e., n ∼ 1. Thus, the observed linear laser-power dependence has been rationalized as being caused by the strong Rabi oscillations between the (2p)-(1s) states.
Symmetry-resolved soft x-ray absorption spectroscopy: its application to simple molecules
Journal of Physics B: Atomic, Molecular and Optical Physics, 2005
This paper reviews our recent progress on the angle-resolved photoion-yield spectroscopic (ARPIS)... more This paper reviews our recent progress on the angle-resolved photoion-yield spectroscopic (ARPIS) technique applied to the K-shell excitations of the simple linear molecules, N2, CO, C2H2, O2, CO2, N2O, OCS and CS2. This spectroscopic technique enables us to distinguish symmetries of electronic states; e.g., the DeltaLambda = 0 parallel and DeltaLambda = ±1 perpendicular transitions for the diatomic molecules can
K-shell photoionization of CO: II. Determination of dipole matrix elements and phase differences
Journal of Physics B: Atomic, Molecular and Optical Physics, 2000
ABSTRACT
Journal of Physics: Conference Series, 2009
We have measured molecular-frame photoelectron angular distributions from carbon 1s and oxygen 1s... more We have measured molecular-frame photoelectron angular distributions from carbon 1s and oxygen 1s levels of CO molecules up to a photoelectron kinetic energy (KE) of ~150 eV. The backward-scattering intensities exhibited a strong modulation as a function of the kinetic energy of the photoelectrons, whereas the intensities for the forward-scattering gradually increased and then became nearly constant over KE ~100 eV. Multiple scattering calculations with a muffin-tin potential qualitatively reproduced the experimental results. The present results may be considered as the observation of low-energy photoelectron diffraction patterns for gaseous free CO molecules, which are involved in modulations in extended X-ray absorption fine structure (EXAFS) spectra.
Journal of Physics: Conference Series, 2009
Double-slit and forward focusing effects in XPD spectra from H2O and GeCl2 molecules have been th... more Double-slit and forward focusing effects in XPD spectra from H2O and GeCl2 molecules have been theoretically studied within the single scattering approximation. In lowand intermediate-energy region, the double-slit effect can be observed. In contrast, this effect wears off and only forward focusing peaks with simple structure are given in high-energy region. The double-slit effects can be observed under special conditions where the two scattering amplitudes have finite overlap in the bisecting direction.
Photoemission dynamics in the molecular frame
Journal of Physics: Conference Series, 2010
ABSTRACT Photoemission dynamics, based on the molecular frame photoelectron angular distribution,... more ABSTRACT Photoemission dynamics, based on the molecular frame photoelectron angular distribution, is reported. In the fast decay channel leading to Ne+ + Ne2+ of Ne2 dimer, the molecular frame photoelectron measurements have been realized, and the core-hole localization observed. However, in the slow decay channel leading to Ne+ + Ne+, such measurements have not been applicable as expected. The molecular frame photoemission study has been extended to a non-axially symmetric H2O molecule, and its experimental result has been well explained by a simple scattering model which is widely used in surface science.
Multiple-scattering calculations for 1s photoelectron angular distributions from single oriented molecules in the energy region above 50 eV
Journal of Electron Spectroscopy and Related Phenomena, 2012
ABSTRACT 1s photoelectron angular distributions from fixed-in-space CO2, NO2, BF3 and CH3F molecu... more ABSTRACT 1s photoelectron angular distributions from fixed-in-space CO2, NO2, BF3 and CH3F molecules have been calculated by X-ray photoelectron diffraction (XPD) theory with muffin-tin-type molecular potential. For all the molecules, the calculated results show good agreements with those by density functional theory in the energy region ≳100 eV. Furthermore, for all the molecules experimental data on the angular distributions in such energy region are well reproduced by the XPD theory. These intensive studies lead to a rather general rule that the XPD theory is an adequate tool to describe high-energy photoelectron angular distributions for any single oriented molecules.
High‐resolution and symmetry‐resolved N and O K‐edge absorption spectra of NO
The Journal of Chemical Physics, 1992
High-resolution electron-yield and ‘‘symmetry-resolved’’ ion-yield spectra have been measured at ... more High-resolution electron-yield and ‘‘symmetry-resolved’’ ion-yield spectra have been measured at the N and O K edges of a 2&Pgr; open-shell molecule, NO. Several Rydberg transitions converging to the 3&Pgr; and 1&Pgr; ionization thresholds are found. The core-to-valence and core-to-Rydberg transitions are interpreted with the help of abinitio self-consistent-field configuration-interaction and frozen-core calculations for the core-excited states with three open shells. It is found that the equivalent-core model (N*O=O2) breaks down in discussing the state ordering of the three N 1s–2pπ* excited states, 2Δ, 2Σ−, and 2Σ+. It is important to consider explicitly the core hole and the exchange repulsion between the core and π* electrons.
Photoelectron–photoion–photoion momentum spectroscopy as a direct probe of the core-hole localization in C 1s photoionization of C2H2
Journal of Physics B: Atomic, Molecular and Optical Physics, 2007
ABSTRACT Angular distributions of C 1s photoelectrons, relative to a dissociation axis for C2H2, ... more ABSTRACT Angular distributions of C 1s photoelectrons, relative to a dissociation axis for C2H2, have been measured with a photoelectron–photoion–photoion coincidence technique. The photoelectron angular distribution (PAD) for three two-body fragmentations (symmetric, non-symmetric and proton-migration fragmentations) is completely different. The PADs for non-symmetric fragmentation provide direct evidence of a localized core-hole and preferential bond breaking following Auger decays. Moreover, the PAD for symmetric fragmentation has been interpreted as the interference between photoemissions from the two carbon atoms.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2011
Three-photon double ionization of an Ar atom has been investigated by photoelectron spectroscopy ... more Three-photon double ionization of an Ar atom has been investigated by photoelectron spectroscopy using an extreme ultraviolet free-electron laser. When the photon energy of the laser has been tuned to the resonances of the intermediate Ar + ion, photoelectron peaks due to the resonant two-photon single ionization of the Ar + ion have been observed. And it has been revealed that the appearance of the peaks is controlled by the mixing ratios of 3p 4 core-configurations of the multi-configuration states. Furthermore, it has been shown that the laser intensity dependence of the Ar 2+ ion production rate due to the resonant two-photon single ionization strongly deviates from that expected by perturbation theory.
The Journal of Chemical Physics
Operando time-resolved soft x-ray absorption spectroscopy (TR-SXAS) is an effective method to rev... more Operando time-resolved soft x-ray absorption spectroscopy (TR-SXAS) is an effective method to reveal the photochemical processes of metal complexes in solutions. In this study, we have developed the TR-SXAS measurement system for observing various photochemical reactions in solutions by the combination of laser pump pulses with soft x-ray probe pulses from the synchrotron radiation. For the evaluation of the developed TR-SXAS system, we have measured nitrogen K-edge x-ray absorption spectroscopy (XAS) spectra of aqueous iron phenanthroline solutions during a photoinduced spin transition process. The decay process of the high spin state to the low spin state in the iron complex has been obtained from the ligand side by N K-edge XAS, and the time constant is close to that obtained from the central metal side by time-resolved Fe K-edge XAS in the previous studies.
The Journal of Physical Chemistry, 1996
Fragment ion yields in the C 1s f Rydberg excitation region of CO 2 were measured in the 90°and 0... more Fragment ion yields in the C 1s f Rydberg excitation region of CO 2 were measured in the 90°and 0°d irections relative to the electric vector of the linearly polarized light. The C 1s f ns (n) 3, 4), npπ and npσ (n) 3-7), and nd (n) 3, 4) Rydberg transitions are clearly observed and show some vibrational structures. The dipole-forbidden C 1s(σ g) f 3sσ g Rydberg transition is the strongest of all the Rydberg transitions, and the ion yield in the 90°direction is dominant. This indicates that the bending vibration is predominantly coupled with the 3sσ g Rydberg state and the intensity-lending dipole-allowed state is a very strong π* resonance, only 2 eV lower than the 3sσ g state. On the other hand, in the 4sσ g Rydberg state the vibronic coupling through the antisymmetric stretching mode is strongly observed in the 0°direction. This is probably because the 4sσ g state approaches another intensity-lending state with Σ u + symmetry and goes away from the π* resonance. The angle-resolved ion-yield technique is very powerful for elucidating the vibronic coupling mechanism.
Angle Resolved Photoion Spectroscopy of Core-Excited Free-Molecules
Fixed-Molecule 1sσg,u Photoelectron Angular Distributions as a Probe of σg* and σu* Shape Resonances of CO2
Physical Review Letters, 1997
ABSTRACT
Physical Review Letters, 1995
The angular distributions of 1sophotoelectrons from N2 molecules held fixed in space have been me... more The angular distributions of 1sophotoelectrons from N2 molecules held fixed in space have been measured around the or* shape resonance for the first time, The angular distributions have been very rich in structure, which are completely different from usual photoelectron angular distributions from randomly oriented molecules, as predicted by Dill. The orbital angular momentum properties of the 1scr photoelectrons around the o. * shape resonance have been made clear from the angular distribution patterns.
Angular Correlation Between B K-VV Auger Electrons of BF3 Molecules and Coincident Fragment Ions: Manifestation of the Difference Between the Angular Correlation and Molecular Frame Auger Electron...
Physical Review Letters, 2013
We have measured the angular correlation between the B K-VV Auger electrons of BF(3) molecules an... more We have measured the angular correlation between the B K-VV Auger electrons of BF(3) molecules and the coincident fragment-ion pairs of BF(2)(+)-F(+). Then, we have found that the measured angular correlation patterns depending on the mutual angle between the light polarization direction and molecular orientation are affected by the anisotropic axis distribution of the molecular ensemble of BF(3)(+) reflecting the anisotropic nature of photon-molecule interaction. In this context, we have pointed out generally that for coincidence experiments, so-called molecular frame Auger electron angular distributions are realized only if the axis distribution of the molecular ion ensemble is isotropic.
Shape-Resonance-Enhanced Vibrational Effects in the Angular Distributions of C 1s Photoelectrons from Fixed-in-Space CO Molecules
Physical Review Letters, 2003
Angular distributions of C 1s photoelectrons from fixed-in-space CO molecules have been measured ... more Angular distributions of C 1s photoelectrons from fixed-in-space CO molecules have been measured with vibrational resolution. A strong dependence of the angular distributions on the vibrational states of the residual molecular ion has been found for the first time in the region of the shape resonance. Calculations in the relaxed core Hartree-Fock approximation have reproduced the angular distributions fairly well in the general shapes of the angular distributions due to the correct description of nuclear motion as an average of the internuclear-distance-dependent dipole amplitudes.
Direct Probe of the Shape Resonance Mechanism in 2σg-Shell Photoionization of the N2 Molecule
Physical Review Letters, 2002
ABSTRACT
Photoelectron Angular Distributions from O K Shell of Oriented CO Molecules: A Critical Comparison between Theory and Experiment
Physical Review Letters, 2000
The dynamical information (ten dipole matrix elements and eight phase differences) has been deduc... more The dynamical information (ten dipole matrix elements and eight phase differences) has been deduced from the measured angular distributions of photoelectrons from O K shell of oriented CO molecules near the ionization threshold in the region of a sigma(*) shape resonance. Light polarization parallel and perpendicular to the molecular axis has been used. An important contribution of six lsigma partial waves with 0</=l</=5 to the sigma(*) shape resonance is demonstrated. A comparison with our calculations in the relaxed core Hartree-Fock approximation reveals only a qualitative agreement, therefore a more advanced theory is needed.
Direct Determination of Partial Wave Contributions in the σ* Shape Resonance of CO Molecules
Physical Review Letters, 1998
ABSTRACT
Physical Review A, 2011
The two-photon resonance ionization probability of atoms in strong extreme-ultraviolet free-elect... more The two-photon resonance ionization probability of atoms in strong extreme-ultraviolet free-electron laser (EUV FEL) pulses has been investigated by the model of time-dependent wave packet propagation of a lightcoupled multilevel atom. Under the simulation within the model assuming single-mode FEL pulses, the ionization probability P ion has shown characteristic dependences on the scaled coupling parameter U gi between two levels of the ground (g) and intermediate (i) resonance states, namely, P ion ∝ (U gi) n , with n being equal to ∼2, less than 1, and ∼1 for the small, medium, and large U gi regimes, respectively. This power dependence of the ionization probability has been interpreted due to Rabi oscillations between g and i states. To compare with recent experimental results on the same condition, the multimode nature of self-amplitude spontaneous emission (SASE) FEL pulses has been managed in the simulation. Then, the recent experimental laser-power dependence of the two-photon resonance ionization of He [Sato et al., J. Phys. B 44, 161001 (2011)] has been well described by that for the large U gi regime of the simulation, i.e., n ∼ 1. Thus, the observed linear laser-power dependence has been rationalized as being caused by the strong Rabi oscillations between the (2p)-(1s) states.
Symmetry-resolved soft x-ray absorption spectroscopy: its application to simple molecules
Journal of Physics B: Atomic, Molecular and Optical Physics, 2005
This paper reviews our recent progress on the angle-resolved photoion-yield spectroscopic (ARPIS)... more This paper reviews our recent progress on the angle-resolved photoion-yield spectroscopic (ARPIS) technique applied to the K-shell excitations of the simple linear molecules, N2, CO, C2H2, O2, CO2, N2O, OCS and CS2. This spectroscopic technique enables us to distinguish symmetries of electronic states; e.g., the DeltaLambda = 0 parallel and DeltaLambda = ±1 perpendicular transitions for the diatomic molecules can
K-shell photoionization of CO: II. Determination of dipole matrix elements and phase differences
Journal of Physics B: Atomic, Molecular and Optical Physics, 2000
ABSTRACT
Journal of Physics: Conference Series, 2009
We have measured molecular-frame photoelectron angular distributions from carbon 1s and oxygen 1s... more We have measured molecular-frame photoelectron angular distributions from carbon 1s and oxygen 1s levels of CO molecules up to a photoelectron kinetic energy (KE) of ~150 eV. The backward-scattering intensities exhibited a strong modulation as a function of the kinetic energy of the photoelectrons, whereas the intensities for the forward-scattering gradually increased and then became nearly constant over KE ~100 eV. Multiple scattering calculations with a muffin-tin potential qualitatively reproduced the experimental results. The present results may be considered as the observation of low-energy photoelectron diffraction patterns for gaseous free CO molecules, which are involved in modulations in extended X-ray absorption fine structure (EXAFS) spectra.
Journal of Physics: Conference Series, 2009
Double-slit and forward focusing effects in XPD spectra from H2O and GeCl2 molecules have been th... more Double-slit and forward focusing effects in XPD spectra from H2O and GeCl2 molecules have been theoretically studied within the single scattering approximation. In lowand intermediate-energy region, the double-slit effect can be observed. In contrast, this effect wears off and only forward focusing peaks with simple structure are given in high-energy region. The double-slit effects can be observed under special conditions where the two scattering amplitudes have finite overlap in the bisecting direction.
Photoemission dynamics in the molecular frame
Journal of Physics: Conference Series, 2010
ABSTRACT Photoemission dynamics, based on the molecular frame photoelectron angular distribution,... more ABSTRACT Photoemission dynamics, based on the molecular frame photoelectron angular distribution, is reported. In the fast decay channel leading to Ne+ + Ne2+ of Ne2 dimer, the molecular frame photoelectron measurements have been realized, and the core-hole localization observed. However, in the slow decay channel leading to Ne+ + Ne+, such measurements have not been applicable as expected. The molecular frame photoemission study has been extended to a non-axially symmetric H2O molecule, and its experimental result has been well explained by a simple scattering model which is widely used in surface science.
Multiple-scattering calculations for 1s photoelectron angular distributions from single oriented molecules in the energy region above 50 eV
Journal of Electron Spectroscopy and Related Phenomena, 2012
ABSTRACT 1s photoelectron angular distributions from fixed-in-space CO2, NO2, BF3 and CH3F molecu... more ABSTRACT 1s photoelectron angular distributions from fixed-in-space CO2, NO2, BF3 and CH3F molecules have been calculated by X-ray photoelectron diffraction (XPD) theory with muffin-tin-type molecular potential. For all the molecules, the calculated results show good agreements with those by density functional theory in the energy region ≳100 eV. Furthermore, for all the molecules experimental data on the angular distributions in such energy region are well reproduced by the XPD theory. These intensive studies lead to a rather general rule that the XPD theory is an adequate tool to describe high-energy photoelectron angular distributions for any single oriented molecules.
High‐resolution and symmetry‐resolved N and O K‐edge absorption spectra of NO
The Journal of Chemical Physics, 1992
High-resolution electron-yield and ‘‘symmetry-resolved’’ ion-yield spectra have been measured at ... more High-resolution electron-yield and ‘‘symmetry-resolved’’ ion-yield spectra have been measured at the N and O K edges of a 2&Pgr; open-shell molecule, NO. Several Rydberg transitions converging to the 3&Pgr; and 1&Pgr; ionization thresholds are found. The core-to-valence and core-to-Rydberg transitions are interpreted with the help of abinitio self-consistent-field configuration-interaction and frozen-core calculations for the core-excited states with three open shells. It is found that the equivalent-core model (N*O=O2) breaks down in discussing the state ordering of the three N 1s–2pπ* excited states, 2Δ, 2Σ−, and 2Σ+. It is important to consider explicitly the core hole and the exchange repulsion between the core and π* electrons.