Anisotropy of the angular distribution of fragment ions in dissociative double photoionization of N2O molecules in the 30–50eV energy range

The double photoionization of N2O molecules by linearly polarized light in the 30-50 eV energy range has been studied by coupling ion imaging technique and electron-ion-ion coincidence. For the two possible dissociative processes, leading to N++NO+ and O++N2+, angular distributions of ionic fragments have been measured, finding an evident anisotropy. This indicates that the molecules ionize when their axis is parallel to the light polarization vector and the fragments are separating in a time shorter than the dication rotational period. The analysis of results provides, in addition to the total kinetic energy of ionic fragments, crucial information about the double photoionization dynamics.

Measurement of the partial photoionization cross sections and asymmetry parameters of S atoms in the photon energy range 10.0–30.0eV using constant-ionic-state spectroscopy

The partial photoionization cross sections and asymmetry parameters of S atoms have been measured using constant-ionic-state (CIS) spectroscopy in the photon energy range 10.0-30.0 eV. The ionizations investigated in these CIS experiments are the (3p)(-1) ionizations S(+)((4)S)<--S((3)P), S(+)((2)D)<--S((3)P), and S(+)((2)P)<--S((3)P). For the first time Rydberg series which converge to the fourth ionization limit have been observed and assignments of these series have been proposed. These correspond to excitations to Rydberg states that are parts of series which converge to the fourth ionization limit, S(+)((4)P)<--S((3)P) (3s)(-1), and autoionize to the lower S(+)((4)S), S(+)((2)D), or S(+)((2)P) states. For each series observed in the CIS spectra photoelectron angular distribution studies, combined with other evidence, has allowed the angular momentum character of the free electron on autoionization to be determined.

Electronic structure of copper phthalocyanine: An experimental and theoretical study of occupied and unoccupied levels

An experimental and theoretical study of the electronic structure of copper phthalocyanine (CuPc) molecule is presented. We performed x-ray photoemission spectroscopy (XPS) and photoabsorption [x-ray absorption near-edge structure (XANES)] gas phase experiments and we compared the results with self-consistent field, density functional theory (DFT), and static-exchange theoretical calculations. In addition, ultraviolet photoelectron spectra (UPS) allowed disentangling several outer molecular orbitals. A detailed study of the two highest occupied orbitals (having a(1u) and b(1g) symmetries) is presented: the high energy resolution available for UPS measurements allowed resolving an extra feature assigned to vibrational stretching in the pyrrole rings. This observation, together with the computed DFT electron density distributions of the outer valence orbitals, suggests that the a(1u) orbital (the highest occupied molecular orbital) is mainly localized on the carbon atoms of pyrrole rings and it is doubly occupied, while the b(1g) orbital, singly occupied, is mainly localized on the Cu atom. Ab initio calculations of XPS and XANES spectra at carbon K edge of CuPc are also presented. The comparison between experiment and theory revealed that, in spite of being formally not equivalent, carbon atoms of the benzene rings experience a similar electronic environment. Carbon K-edge absorption spectra were interpreted in terms of different contributions coming from chemically shifted C 1s orbitals of the nonequivalent carbon atoms on the inner ring of the molecule formed by the sequence of CN bonds and on the benzene rings, respectively, and also in terms of different electronic distributions of the excited lowest unoccupied molecular orbital (LUMO) and LUMO+1. In particular, the degenerate LUMO appears to be mostly localized on the inner pyrrole ring.

Valence photoionization dynamics in circular dichroism of chiral free molecules: the methyl-oxirane

The dynamical behavior of circular dichroism for valence photoionization processes in pure enantiomers of randomly oriented methyl-oxirane molecules has been studied by circularly polarized synchrotron radiation. Experimental results of the dichroism coefficient obtained for valence photoionization processes as a function of photon energy have been compared with theoretical values predicted by state-of-the-art ab initio density-functional theory. The circular dichroism measured at low electron kinetic energies was as large as 11%. Trends in the experimental dynamical behavior of the dichroism coefficients D(i)(omega) have been observed. Agreement between experimental and theoretical results permits unambiguous identification of the enantiomer and of the individual orbitals.

Magnetic-field induced enhancement in the fluorescence yield spectrum of doubly excited states in helium

An influence of static magnetic fields on the fluorescence yield spectrum of He in the vicinity of the N = 2 thresholds has been observed. The experimental results are in excellent agreement with predictions based on multichannel quantum defect theory, and it is demonstrated that the Rydberg electron l mixing due to the diamagnetic interaction is essential for the description of the observed fluorescence yield intensity enhancement.

The double photoionization of hydrogen iodide molecules

The double photoionization of HI molecules has been investigated using vacuum ultraviolet synchrotron radiation in the energy range between 27 and 35 eV. The product ions have been detected by the use of time-of-flight mass spectrometry and the threshold energy for HI2+ and H+ + I+ formation has been determined. These results have been interpreted by the use of a theoretical model which has been previously applied by us to HBr2+ and HCl2+. On the basis of the reliability of such a model, an assessment of the systematic trends of the bond features along the HX2+ (X=F, Cl, Br, I) homologous series is given in this paper. In particular, the increase of the stability of these dications, in their lowest electronic states, when going towards the heavier molecules, has been rationalized considering the systematic variation of the charge transfer coupling between the H-X2+ and the H+-X+ states.

Double excitations of helium in weak static electric fields

A dramatic electric field dependence has been observed in the fluorescence yield spectrum of the doubly excited states in helium, where a rich phenomenology is encountered below the threshold. Fluorescence yields of certain states can be tuned to zero, while other dipole-forbidden states are significantly enhanced, for fields much weaker than 1 kV/cm. Using an R-matrix multichannel quantum defect theory, spherical-to-parabolic frame transformation method, we are able to reproduce the main features of the observed spectrum, and we discuss the qualitative behavior in terms of weak electric field mixing.

Angle-Resolved Photoelectron Spectroscopy of Randomly Oriented 3-Hydroxytetrahydrofuran Enantiomers

Circular dichroism in the angular distribution of valence photoelectrons emitted from randomly oriented 3-hydroxytetrahydrofuran enantiomers (ThS and ThR) has been observed in gas-phase experiments using circularly polarized vacuum ultraviolet (VUV) light. The measured dichroism for both ThS and ThR, acquired at the single magic angle theta=234.73 degrees and at photon energies of 22, 19, 16, and 14 eV, points to an asymmetric forward-backward scattering of the photoelectrons from their highest occupied molecular orbitals (HOMO) HOMO-1 and HOMO-2, of up to 5%, depending on the photon energy. The asymmetry reverses on exchange of either the helicity of the radiation or the configuration of Th. The photoionization dichroic D parameters of ThS and ThR have been measured and their values discussed in the light of LCAO B-spline density functional theory (DFT) predictions. While an acceptable agreement is found between the dichroic parameter measured and calculated at the highest photon energy for the HOMO and HOMO-2 orbitals of Th, a significant discrepancy is observed for the HOMO-1 state which is attributed to the floppiness of Th, in particular to the comparatively large sensitivity of the size and shape of its HOMO-1 on nuclear vibrational motion.

Core-shell photoabsorption and photoelectron spectra of gas-phase pentacene: Experiment and theory

The C K-edge photoabsorption and 1s core-level photoemission of pentacene (C22H14) free molecules are experimentally measured, and calculated by self-consistent-field and static-exchange approximation ab initio methods. Six nonequivalent C atoms present in the molecule contribute to the C 1s photoemission spectrum. The complex near-edge structures of the carbon K-edge absorption spectrum present two main groups of discrete transitions between 283 and 288 eV photon energy, due to absorption to pi* virtual orbitals, and broader structures at higher energy, involving sigma* virtual orbitals. The sharp absorption structures to the pi* empty orbitals lay well below the thresholds for the C 1s ionizations, caused by strong excitonic and localization effects. We can definitely explain the C K-edge absorption spectrum as due to both final (virtual) and initial (core) orbital effects, mainly involving excitations to the two lowest-unoccupied molecular orbitals of pi* symmetry, from the six chemically shifted C 1s core orbitals.

The double photoionization of HCl: An ion–electron coincidence study

The double photoionization of HCl molecules by synchrotron radiation has been studied in the energy range between 30 and 50 eV. The HCl(2+) and Cl(2+) product ions have been detected by a photoelectron-photoion-coincidence technique, while the H(+)+Cl(+) formation, which follows the double ionization of HCl, has been studied by photoelectron-photoion-photoion coincidence. The photon energy threshold for the production of HCl(2+) ions has been found to be 35.4+/-0.6 eV, while for the dissociative channel leading to H(+)+Cl(+), it has been measured a threshold at 36.4+/-0.6 eV and a change in the slope of the cross-section energy dependence at 38.7+/-0.7 eV. The production of H+Cl(2+) occurs with a threshold photon energy of 42.8+/-1.1 eV. These results appear to be in a good agreement with previous data by different experimental techniques and recent theoretical calculations performed by our laboratory.

Self-rated measures of physical activity and cardiovascular risk in a sample of Southern Italian male workers: the Olivetti heart study

BACKGROUND AND AIM

The number of people who are overweight, obese and/or lead a sedentary lifestyle is increasing, and numerous studies have shown that physical activity has beneficial cardiovascular effects.

METHODS

The aim of this study was to evaluate the relationship between physical activity and the anthropometric, cardiovascular and metabolic variables involved in coronary risk. The study population consisted of 1075 adult men aged 25-75 years, all of whom were workers in Olivetti factories. Physical activity was assessed by means of a questionnaire and the sample was divided into two groups: those practising sport and those who said they were sedentary.

RESULTS

Age-adjusted BMI was higher in the participants practising sport, whereas the values of all of the remaining variables (i.e. abdominal circumference, skinfolds, heart rate, blood pressure, serum cholesterol, triglyceride, glucose, insulin and HOMA) were lower; however, the only statistically significant differences were in heart rate and blood pressure. After the subjects were classified as being normal weight, overweight or obese on the basis of BMI, the active participants tended to have lower values for all of the parameters than their sedentary counterparts in each BMI category. In a subgroup undergoing OGTT, glucose and insulin levels at T0 and T60 were significantly lower in the active participants.

CONCLUSIONS

These findings confirm the usefulness of physical activity in preventing cardiovascular disease.

Low-lying electronic states of HBr2+

The present study describes the characterization of energy and structure of HBr(2+) in its low-lying electronic states, achieved through an extension of a new empirical method [Chem. Phys. Lett. 379, 139 (2003)] recently introduced to evaluate the interatomic interaction in the HX(2+) (X=F,Cl,Br,I) molecular dications. The method is based on identification of the main components of the interaction and their evaluation through some simple correlation formulas. Potential energy curves, given in a simple, natural, and analytical form, made possible the calculations of some important properties, such as double-photoionization energy thresholds, vibrational spacing, average lifetime, and Franck-Condon factors. The predictions, compared with data available in the literature, are of great interest for the analysis and interpretation of some new experimental results.

Threshold-photoelectron-spectroscopy-coincidence study of the double photoionization of HBr

A threshold-photoelectron-coincidence spectrum of HBr has been recorded in the 32.2-35.8 eV photon energy range, with a resolution of approximately 0.01 eV, using a synchrotron radiation source. The X (3)Sigma(-) and a (1)Delta(2) states of the HBr(2+) dication are clearly observed in the spectrum, while there is no clear evidence for the formation of the b (1)Sigma(+) electronic state. For the first two states, the vibrational states v=0-3 have been resolved, while for the ground X (3)Sigma(-) state also spin-orbit splitting has been detected. The results appear in good agreement with previous experimental observations. A comparison with theoretical predictions indicates the role of "noncovalent" contributions to the interaction between the two atomic partners for the formation of metastable states.

Natural history of chronic viral hepatitis in southern Italy: epidemiological changes since the introduction of the anti-HCV test

We investigated whether there are differences between the natural history of B and C chronic hepatitis in a southern Italian population, and whether the chronic viral hepatitis population was modified by the introduction of the anti-HCV test in 1989. We examined clinical charts of 1120 patients consecutively admitted to our division from January 1979 to December 1998 with the histological diagnosis of chronic viral hepatitis (304 from 1979 to 1988; 816 from 1989 to 1998). We found significant differences only in age at diagnosis (higher in the second decade, P = 0.001), and in aetiology (HBV decreased in the second decade, P < 0.0001). We were able to follow up 449 patients for 2-20 years (311 with HCV and 138 with HBV infection), and found that chronic HCV evolved to cirrhosis more frequently than did chronic HBV; but in both types time to development of cirrhosis and the incidence of death were similar. Our data confirm that a higher onset age of HBV and of HCV is frequently observed in those subjects who have a faster disease progression.

[A new model of health surveillance: lessons learned from epidemiology]

Occupational medicine in the last few years is trying to tune its objectives to the changing needs of the working world. The continuous reduction of incidence of work related diseases progressively substituted with chronic degenerative ones, suggests a different strategy to prevent occupational diseases and to protect workers health. Health surveillance should not be limited only to draw up the work qualification but should be the starting point to plan intervention useful both to workers and to the general population. Corner stone of this endeavour is the epidemiological research focused on the improvement of quality of life.

Experimental determination of the lifetime for the 2p3d(1P0) helium doubly excited state

Two recent theoretical studies [C. Liu, Phys. Rev. A 64, 010501 (2001)]; M. Zitnik, ibid. 65, 032520 (2002)]] predict that the fluorescence lifetimes of helium doubly excited states converging to He+ N=2 should be longer than that of the He+ 2p ion state. This effect is caused by the electric field of the outer electron which, through Stark mixing, gives the inner fluorescing electron some series specific, stabilizing 2s character. We have obtained the first experimental evidence that confirms this effect by measuring the lifetime of the 2p3d(1P0) doubly excited state. This was determined to be 190+/-30 ps compared to 100 ps for the He+ 2p ion state. The measurements were performed using short pulses of synchrotron radiation to form doubly excited states and recording the arrival time of photons from fluorescence.