Experimental and theoretical study of the electronic states and spectra of PbLi

Gas phase emission spectra of the hitherto unknown free radical PbLi have been measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast flow system in which lead vapor in argon carrier gas was passed through a microwave discharge and mixed with lithium vapor in an observation tube. Five electronic transitions have been found in the wavenumber range 3800-10 000 cm⁻¹. Bands from two excited states to the ground state were measured at high spectral resolution such that rotational analyses could be performed and accurate molecular parameters derived. In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential curves for the low-lying states of PbLi and also electric dipole transition moments connecting them. As in the lighter molecules of this group, CLi and SiLi, the ground state of PbLi is found to be 3/2) with a spin splitting of about 2000 cm⁻¹. The first excited state is (A 1/2), and two observed band systems are assigned to the transitions A→X₁ and A→X₂. Two more excited states, (B 3/2) and C 1/2, are identified from the observed spectra with the help of the computed data, and their spectroscopic constants are determined. In contrast to PbH and PbF, the ab initio results indicate a very complicated low-energy electronic structure for the PbLi radical, with 19 bound electronic states calculated to lie below 3 eV.     

Experimental and Theoretical Study of the Electronic States and Spectra of TeH and TeLi

Gas-phase emission spectra of the hitherto unknown free radical TeLi have been measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast flow system in which tellurium vapor in argon carrier gas was passed through a microwave discharge and mixed with lithium vapor in an observation tube. Two systems of blue-degraded bands were measured at high spectral resolution in the ranges 8000-9000 and 5700-6700 cm(-1) and vibrational and rotational analyses were performed. In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential curves for the low-lying states of TeLi and the isovalent TeH and also electric dipole transition moments connecting them. As in the TeH system, the ground state of TeLi is found to be X(2)Pi(i), but with a remarkably smaller spin-orbit splitting. The TeLi calculations indicate a strongly bound A(2)Sigma(+) state, while in TeH the analogous state is computed to lie significantly higher at approximately 32 000 cm(-1), and it is strongly predissociated. Based on the theoretical analysis, the observed TeLi band systems are assigned to the transitions A(2)Sigma(+)(A1/2)-->X(1)(2)Pi(3/2)(X(1)3/2) and A(2)Sigma(+)(A1/2)-->X(2)(2)Pi(1/2)(X(2)1/2). Analysis of the spectra has yielded the molecular constants (in cm(-1)) X(1)(2)Pi(3/2):omega(e)=457.49(3), omega(e)x(e)=2.482(9), B(0)=0.408908(8); X(2)(2)Pi(1/2): T(e)=2353.44(3), omega(e)=456.28(4), omega(e)x(e)=2.635(8), B(0)=0.414954(8), p(0)=1.00637(4); A(2)Sigma(+): T(e)=8574.64(2), omega(e)=437.81(3), omega(e)x(e)=2.581(8), B(0)=0.423903(8), p(0)=-0.19915(2), where the numbers in parentheses are the standard deviations of the parameters. Comparison of the isovalent TeLi and TeH systems emphasizes that the difference in bonding character (ionic in TeLi vs covalent in TeH) is responsible for qualitative differences in the electronic spectra of these two molecules. Copyright 2001 Academic Press.     

GUIDELINES FOR WHOLE-BODY VIBRATION HEALTH SURVEILLANCE

There is strong epidemiological evidence that occupational exposure to WBV is associated with an increased risk of low back pain (LBP), sciatic pain, and degenerative changes in the spinal system, including lumbar intervertebral disc disorders. A prototype health surveillance scheme for WBV is presented in this paper. Surveillance is the collection, analysis, and dissemination of data for the purpose of prevention. The aims are to assess health status and diagnose vibration-induced disorders at an early stage, to inform the workers on the potential risk associated with vibration exposure, to give preventive advice to employers and employees and to control whether preventive measures which have been taken, were successful. It is suggested that a pre-placement health examination should be offered to each worker who will be exposed to WBV so as to make the worker aware of the hazards, to obtain baseline health data, and to identify medical conditions that may increase the risk due to WBV. The case history should focus on personal history, work history, and leisure activities involving driving of vehicles. The personal medical history should detail back pain complaints, disorders in the spine, any injuries or surgery to the musculoskeletal system. A physical examination on the lower back should be performed on workers who have experienced LBP symptoms over the past 12 months. The preplacement examination should be followed by periodic health reassessment with a regular interval according to the legislation of the country. It is suggested that periodic medical examination should be made available at least every 2 years to all workers who are exposed to WBV. Any change in vibration exposure at the workplace should be reported by the employer. If an increase in vibration exposure or a change in health status have occurred, the medical re-examination should be offered at shorter intervals at the discretion of the attending physician. There should be a periodic medical examination, which includes recording any change in exposure to WBV. The findings for the individual should be compared with previous examinations. Group data should also be compiled periodically. Medical removal may be considered along with re-placement in working practices without exposure to WBV. This paper presents opinions on health surveillance for whole-body vibration developed within a working group of partners funded on a European Community Network (BIOMED2 concerted action BMH4-CT98-3251: Research network on detection and prevention of injuries due to occupational vibration exposures). The health surveillance protocol and the draft questionnaire with explanation comments are presented for wider consideration by the science community and others before being considered appropriate for implementation.     

New coumarin from the roots of Prangos pabularia

The new coumarin 1, yuganin A (7-methoxy-8-((1S,2S)-1,2,3-trihydroxy-3-methylbutyl)-2H-chromen-2-one) along with nine known coumarins, heraclenol 3′-O-β-D-glucopyranoside (2), oxypeucedanin hydrate 3′-O-β-D-glucopyranoside (3), heraclenol (4), oxypeucedanin hydrate (5), osthole (6), oxypeucedanin (7), heraclenin (8), isoimperatorin (9), imperatorin (10) and the disaccharide sucrose (11), have been isolated from the roots of Prangos pabularia, and the structures of these isolated compounds were elucidated by spectroscopic means, especially, UV, HR-ESIMS, and 1D and 2D NMR spectroscopy. Furthermore, the anti-melanogenic effect of yuganin A and its inhibitory effect on B16 cells were evaluated. Yuganin A may be useful in the treatment of hyperpigmentation and as a skin-whitening agent in the cosmetics industry.     

On the thermodynamic equilibrium between ice and electrolyte solutions in the conditions of confined geometry

For a small volume (of about 10⁻⁶ cm³) of NaCl and other electrolyte solutions (C = 0.1 and 1 M) in thin (r = 5/10 μm) single quartz capillaries, dependencies of the column length l of frozen solutions on the temperature t were measured using comparator IZA-2 in a thermostated chamber. At temperatures range t > −4 °C (for C = 0.1 M) and t > −8 °C (for C = 1 M) the l(t) dependencies are reversible and therefore correspond to establishment of an equilibrium between ice-1 and the solution.

From the constants mass condition of the dissolved salt in a frozen column, the l(t) expression was derived, which includes thermodynamic relation between solution concentration in an equilibrium with ice, C_s, and the temperature t for bulk systems. Deviations from the data known for bulk solutions were observed in thin capillaries when temperature t decreased to −3 °C (for 0.1 M NaCl) and to −6 °C for 1 M NaCl solution.

This effect may be a result of strong adhesion of the ice column to capillary walls. In this case, some internal stresses arise in frozen solution resulting in a deviation from thermodynamic equilibrium conditions for bulk systems. When approaching the temperature of ice melting, adhesion forces decrease due to formation of a thin non-freezing water interlayer on the capillary wall. In this temperature range the experimental data are in agreement with the predictions for bulk systems. It was supposed that the observed deviation in thin capillaries may be caused by formation of an amorphous ice phase with higher density as compared with the ice-1 during rapid freezing, or by an effect of ice microlenses formation. Both effects will result in a deviation from the phase diagram corresponding to a bulk solution.