A combined high-resolution (6 meV) HeI photoelectron (PE) and ab initio theoretical study of the A 2Σ+ ion system of HI and DI has been conducted to elucidate the origin of a peculiar “holelike” feature in the vibrational distribution found in the high-resolution (6 meV) threshold photoelectron (TPE) spectrum of HI. The PE and TPE spectra were found to yield essentially identical results. Ab initio potential energy curves for the low-lying cationic states of HI have been calculated for the first time with and without spin–orbit contributions included. It has been found that the diabatic A 2Σ+ state of HI+ is strongly predissociated due to spin–orbit coupling with the Σ−4, Σ−2, and Π4 repulsive states leading to a complex set of adiabatic curves. It is shown that the adiabatic A 2Σ1/2+ state is only slightly bound (by 260 cm−1 after suitable adjustments of the positions of the various repulsive potentials relative to that of the A state are made based on observed atomic spectral data) and should support at most one vibrational level in both HI+ and DI+. However, using the complex rotational method, it was possible to calculate the energies, predissociation linewidths, and rotational constants of a number of nonstationary vibrational levels (or resonances) of the A 2Σ1/2+ state. Reasonably good agreement has been found between experiment and theory. The observed “hole” in the TPE and PE spectra is attributed to the fact that the stability of the v+=1 and 2 levels is notably less than for v+=0 in the A 2Σ1/2+ state of both HI+ and DI+.

We report temperature-dependent photoelectron spectra for a monolayer of C60 adsorbed on HOPG, as well as C 1s x-ray absorption. This extends a previous report which showed the close similarity between the spectrum of the HOMO for the two-dimensional overlayer and that of C60 in the gas phase. The present work shows that intermolecular and molecule-substrate vibrations contribute strongly to the spectral lineshape at room temperature. Thus, vibrational effects are shown to be crucial for the proper understanding of photoelectron spectra, and thus the charge transport properties, for C60 in contact with graphite and graphite-like materials.

We have recorded very-high-resolution photoelectron spectra of the inner-valence structure of CO+, excited with synchrotron radiation, and have resolved fine structure never previously observed. Recently presented resonant Auger decay spectra (Sundin et al. 1997 Phys. Rev. A56 480, 1997 J. Phys. B: At. Mol. Opt. Phys. 30 4267) have established the energy of two-hole one-particle Rydberg states, and a comparison with these has been made to explain some details of the spectra.

We have recorded angle-resolved He I photoelectron spectra of the three outermost valence states in Nz with high enough resolution to observe rotational lime profiles. For the two Sigma states, the X (2)Sigma(g)(+) and the B (2)Sigma(u)(+), we found that the rotational branches corresponding to different changes in rotational quantum number can differ dramatically in beta value. The well-known difference in beta value for the nu = 0 and nu = 1 vibrations of the X (2)Sigma(g)(+) State was found to be due to different rotational branching ratios and also different beta values of the rotational branches. For the nu = 0 - 2 vibrations of the A (2)Pi(u) state, the beta value difference between rotational branches is much less pronounced than in the X and B states. We have also recorded synchrotron-radiation-excited photoelectron spectra of the nu = 0 vibrational peaks of the X (2)Sigma(g)(+) and B (2)Sigma(u)(+) states where rotational line profiles are resolved. The intensities of the rotational branches were studied as function of photon energy, the X state between 23 and 65 eV, and the B state between 23 and 45 eV. The results for the X state have recently been presented in a Letter [G. Ohrwall, P. Baltzer, and J. Bozek, Phys. Rev. Lett. 81, 546, 1998]. The rotational branching ratios of the two states have very different behaviors as functions of photon energy. The relative intensities of the rotational branches in the X state change significantly over the studied energy range. The 3 sigma(g) --> k sigma(u) shape resonance apparently gives rise to a non-Franck-Condon-like behavior for the rotational branching ratio of the X state. In the B state, the rotational branching ratios remain essentially constant over the studied energy range. [S1050-2947(99)07903-2].

The absolute photoabsorption, photoionization and photodissociation cross sections and the photoionization quantum efficiency of ammonia and deuterated ammonia have been measured from the ionization threshold to 25 eV using a double ion chamber and monochromated synchrotron radiation. The photoabsorption spectrum displays extensive vibrational progressions associated with Rydberg series converging onto excited vibrational levels of the (X) over tilde (2)A(2)" state. New structure has been observed for ND3 in the 10.0-11.3 eV range, and vibrational progressions due to transitions into the (E) over tilde, (F) over tilde and (G) over tilde Rydberg states have been recorded with improved resolution. Features have been observed, for the first time, in the photoabsorption spectra of NH3 and ND3 due to Rydberg series converging onto the (A) over tilde E-2 ionization threshold, and interpretations for some of these features have been proposed based upon the corresponding photoelectron spectra.The He I excited NH3+ (1a(2)")(-1) (X) over tilde (2)A(2)" photoelectron band has been studied experimentally at a resolution of 3 meV and two vibrational progressions, each involving excitation of the nu(2)(+) mode, have been observed. The vibrational lines in the main progression show a complex structure associated with rotational excitations. This structure changes gradually in a way that can be explained by the variation of the H-N-H bond angle with the nu(2)(+) mode. The effective bond angle has been found to be 120 degrees for nu(2)(+) = 0, and simiiar to that of the neutral ground state near nu(2)(+) = 6. The second progression, of weak lines, has been interpreted tentatively as being due to n nu(2)(+)+nu(4)(+). The nu(4)(+) mode is doubly degenerate and the excitation of a single quantum hits been explained by vibronic coupling with the (A) over tilde E-2 state. In addition, He II excitation has been used to record the. entire valence shell photoelectron spectrum.

We have recorded an Auger decay spectrum of the resonantly excited Xe 4d5/2−16p state between 36.4 and 37.3 eV kinetic energy. The spectrum was obtained under resonant Raman conditions, with a bandwidth of ≈6 meV for the exciting radiation, much smaller than the natural lifetime width of 110–120 meV. The full width at half maximum of the peaks in the spectrum was 10 meV, making it possible to completely resolve structure that overlapped in earlier studies.

A photoelectron spectrum of the X2B1[v′=(0,0,0)] state of H2O+ has been recorded, excited with He I radiation. The line profile exhibits extensive rotational structure, and a simple analysis based on the ground-state rotational population is used to interpret the spectrum. Judging from this analysis, c-type transitions account for the dominant part of the intensity.

The rotational branching ratio in the photoelectron spectrum of has been investigated using synchrotron radiation. At the photon energy , the S branch has a considerably higher relative intensity than when excited with He I (, or with Ne I (, ) radiation.

Photoelectron spectra of HCN and DCN have been recorded at a resolution of 4.5 meV or better using HeI and HeII radiation;Ind have been interpreted by comparison with high-level electronic structure calculations. The calculations predict that HCN+ in the (B) over tilde state, previously thought to be linear, is bent at equilibrium. The spectrum for this state shows strong excitation of the C-H stretching mode and the bending mode. both with frequencies much lower than in neutral HCN. A new satellite state with resolved vibrational structure is found at 22.5 eV, and another new state is seen at 33 eV. The dissociation pathways of HCN+ in (B) over tilde and higher states have been determined by photoelectron-photoion coincidence spectroscopy. There is competition between H+ and CN+ production from most of the resolved levels of the (B) over tilde state above the CN+ threshold: the diatomic products have little vibrational energy. Both the sharp vibrational structure and the competition show that predissociation is slow; the calculations indicate the existence of a barrier, preventing direct dissociation. (C) 1998 Elsevier Science B.V.

The absolute photoabsorption, photoionisation and photodissociation cross sections and the photoionisation quantum efficiency of ethylene and deuterated ethylene have been measured from the ionisation threshold to 500 Angstrom using a double ion chamber and monochromated synchrotron radiation. High resolution photoelectron spectra of the same molecules have been recorded using HeI and HeII, radiation, and detailed analyses have been made of the vibrational structure exhibited in the (XB3u)-B-2, A(2)B(3g), B(2)A(g), (CB2u)-B-2 and (DB1u)-B-2 photoelectron bands. In the inner valence binding energy region the HeII excited spectrum shows several satellite features which are due to configuration interaction effects. The photoabsorption spectra display extensive vibrational structure extending from the ionisation threshold to approximately 630 Angstrom. With the aid of the high resolution photoelectron spectra, many of these absorption features have been arranged into vibrational progressions associated with Rydberg states, Tentative assignments for some of these states have been proposed based upon an assessment of term values and quantum defects. A sum rule analysis has been carried out by combining the present absolute photoabsorption measurements with similar data covering the remaining wavelength regions.

We have recorded an angle-resolved photoelectron spectrum of the first four vibrational peaks of the X (2)Sigma(g)(+) state of H-2(+). In the spectrum, the individual peaks of the Delta N=0 rotational branch are completely resolved. From curve fitting of the rotational branches, we found the anisotropy parameter of the /<(mu)over bar>(0,0)/(2) squared reduced multipole moment matrix element to be beta=1.85, with no significant difference between the vibrational states. For the /<(mu)over bar>(2,0)/(2) squared reduced multipole moment matrix element, we found beta(v=0) = 0.83, decreasing slightly at higher vibrational levels. The earlier observed increase in the beta parameter with vibrational quantum number is mainly explained by a decreased size of /<(mu)over bar>(2,0)/(2) relative to /<(mu)over bar>(0,0)/(2), dominating the beta decrease of the /<(mu)over bar>(2,0)/(2) squared reduced multipole moment matrix element itself. We have also determined the beta value of individual peaks in the Delta N=0 branch. The difference in beta between the peaks in this branch is small. In particular, the 0-0 transition does not seem to have a considerably higher beta value than the other members of the Delta N=0 branch, which is expected from theory.

The complete valence shell photoelectron spectrum of the NO2 molecule has been studied in the binding energy range between 10 and 50 eV. HeI and HeII resonance radiation as well as monochromated synchrotron radiation have been used for the ionisation. Assignments have been made for most of the photoelectron bands by comparison with previous theoretical predictions. Photoelectron angular distributions and branching ratios for the bands associated with the outer valence shell have been determined for photon energies between 18 and 120 eV. The HeI and HeII excited spectra have allowed detailed studies to be made of the vibrational fine structure. For the X1Σ+g ground ionic state, close lying vibrational lines associated with combined excitations of the symmetric ν1 and the bending ν2 modes have been observed for the first time. Excitation of the asymmetric stretch ν3 mode, in one quantum, is found in the A1A2 photoelectron band, and its presence is explained in terms of vibronic coupling.

Rotational line profiles have been studied as a function of photon energy by use of photoelectron spectroscopy. The relative squared multipole moment matrix elements of the X (1)Sigma(g)(+) (nu = 0) --> X 2 Sigma(g)(+) (nu = 0) transition of N-2 have been determined from the relative intensities of rotational branches for photon energies between 23 and 65 eV. The; relative intensities, and hence the multipole moment matrix elements of the rotational branches, are clearly dependent on photon energy. This non-Franck-Condon-like behavior can be explained by a shape resonance in the 3 sigma(g) --> k sigma(u) ionization channel.

The photoelectron spectrum of ICN has been remeasured with much higher resolution than before. The main bands are vibrationally analysed and are reconciled with the ICN+ ion emission spectrum. The spectrum has several very unusual features; one possible interpretation is that strong perturbations affect the A2Σ+ and B2-Π ionic states.

We present photoelectron spectra for the highest occupied molecular orbital (HOMO) of C60 in the gas phase and a two-dimensional (2D) condensed layer. For low temperatures the similarity in the spectra is striking and places a strict upper limit of 0.07 eV on the HOMO electronic bandwidth for the 2D solid, which is a fraction of the theoretically predicted value. This is shown to be consistent with expectations of a polaronic model for the bands and suggests the need fora reassessment of the band dispersions in 3D C60.

Angle-resolved photoelectron spectra encompassing the and the states of sulphur hexafluoride have been recorded in the 20 - 22 eV photon energy range using synchrotron radiation. The envelope of the photoelectron band displays a complicated structure which varies significantly both as a function of excitation energy and as a function of electron ejection angle. The data for the state have been analysed by dividing the band into eight regions, specified by their binding energies. The results show that, as the photon energy is varied, the branching ratio for each region exhibits an enhancement at an electron kinetic energy of about 2.5 eV. The photoelectron angular distributions also vary significantly across the band. Various interpretations for this resonant behaviour are discussed.

The HeI excited photoelectron spectrum of the CO2 molecule covering the X 2Πg and A 2Πu ionic states has been recorded at a resolution of better than 5 meV. Complex vibrational structures are resolved in both photoelectron bands. In the X 2Πg state, the ν2 and ν3 modes are observed to be excited in both an odd and even numbers of quanta in addition to the ν1 mode, whereas for the A 2Πu state the spectrum is dominated by excitations of the ν1 mode alone and in combinations with excitations of the ν2 mode in two quanta involving strong Fermi resonance. The observed spectrum has been assigned by comparison with optical spectra and with calculations of the vibrational fine structure including vibronic and spin–orbit coupling.

The complete valence shell photoelectron spectrum of sulphur hexafluoride has been studied using HeII and synchrotron radiation. The high resolution HeII excited spectrum has allowed a detailed analysis to be made of the vibrational structure exhibited in the photoelectron bands associated with ionisation from the outer valence orbitals. New vibrational structure has been observed in the C 2Eg and the F2A1g photoelectron bands. The spectra recorded with synchrotron radiation demonstrate that shape resonance phenomena affect the photoionisation dynamics, and clear evidence is provided for both the t2g and the eg shape resonances. However, the results show that photoelectrons associated with gerade symmetry orbitals also exhibit resonant behaviour, and this is discussed in terms of interchannel coupling and the possibility that the t1u shape resonance might occur above threshold for valence shell ionisation. An essentially structureless photoelectron intensity distribution is observed throughout the entire region for binding energies greater than 25 eV, and this suggests a strong coupling to continuum states. A perturbative Green's function method has been employed to evaluate the ionisation energies and pole strengths associated with the six outermost molecular orbitals, and the results show an improved agreement with the experimental values.