The dissociation of excited state Br2 is probed with the novel technique of ultrafast soft x-ray photoelectron spectroscopy. Excited Br2 molecules are prepared in the dissociative (1)Pi(u) state with 80 fs, 400 nm pulses, and a series of photoelectron spectra are obtained during dissociation with pulses of soft x-ray light (47 nm, 26.4 eV, 250 fs). The formation of Br atoms is readily detected and the data support an extremely fast dissociation time for Br2 on the order of 40 fs. Amplitudes of the pump-probe features reveal that the ionization cross section of atomic Br at 47 nm is approximately 40 times larger than that of Br2.
'Volumes and surface areas of 45 kidneys were determined ultrasonographically in vivo before autopsy and in a water bath phantom after autopsy by means of both the ellipsoid and the stepped section methods.Comparison of results revealed that renal volume may be determined by the simplest method, the ellipsoid method, with sufficient accuracy for clinical use. Results also revealed that renal mass expressed in grams may be directly obtained from renal volume expressed in milliliters, but mass in grams was found to correlate better with renal surface area than with renal volume. A formula relating renal mass to both volume and surface area was developed from regression analysis of the data and was found to provide a more precise e stimate of renal mass than does mass computed from either volume or surface area alone. (Key words: renal volume, renal surfilce area, renal mass) Changes in renal mass accompanied by changes in renal architecture are easily detected by vis ual inspection of ultrasonographic image s. Diseases that result in alterations of renal mass without significant alterations in architecture require a quan• titative method of detection. Renal volume has been used to detect such conditions. This study compares two popular method:; of volume determination and provides a method for computing renal mass. MATERIALS AND METHODSVolumes of 45 kidneys were determined ul· trasonographically by means of the ellipsoid method and the stepped section method.The ellipsoid method assumes that the shape of the structure studied approximates the shape of a prolate ellipsoid ( fig. 1). Volume (V) was determined from the greatest measurements of length (L), width (W), and thickness (T) as related by the following formula: Each linear measurement was performed three times, and the average value used for computation.The s tepped section method requires multiple parallel sections (fig. 2). The area of the structure of interest in each plane was determined by u manual planimeter and multiplied hy the section interval, which was 0.5 em in this study. The total volume wns the sum of the individual section volumes. Each area measurement was performed three times, and the average was used. Volumes were calculated from ultrasonograms obtained in longitudinal and transverse planes, and an average was obtained.Ultrasonograms were obtained in vivo before autopsy and in a water bath phantom following autopsy. Renal volumes obtained by each method were compared with each other and with renal masses. Assuming ellipsoid geometry, surface area varies as the two-thirds power of volume; thus, an effective renal surface area (SA) was defined as follows:where L, W, and T are greatest measurements of renal length, width, and thickness in three orthogonal planes. Regression analysis was performed on the data to determine the best method to compute renal mass. 151
A laser-based instrument is described for the study of femtosecond dissociation dynamics of gas phase molecules via time-resolved vacuum ultraviolet and soft x-ray photoelectron spectroscopy. Visible or UV pump pulses are generated with nonlinear crystal techniques on a Ti:sapphire laser output, while soft x-ray probe pulses are created via high-order harmonic generation of the same laser in rare gases. Here we describe the optical layout of the pump-probe system, the means for separation of the high-order harmonics in the soft x-ray probe beam, including a description of the two grating setup used to compress the high-harmonic pulses and the magnetic bottle photoelectron spectrometer used for data collection. The feasibility of using the generated high-harmonic pulses for an array of gaseous phase photoelectron spectroscopy experiments is established. These include measurements of valence shell and core-level photoelectron transitions in atoms and molecules, the tunability of the soft x-ray harmonic through Rydberg resonances, and the energy bandwidths of the harmonics. Cross correlations between the visible/UV and soft x-ray pulses, by above threshold ionization, are used to establish the pulse timing, pulse duration, and spatial overlap for ultrafast studies. The observed real time photodissociation of Br2 serves as a demonstration of the pump-probe ultrafast technique and the applicability to ultrafast time-resolved chemical dynamics.
Transient photoelectron spectroscopy of the dissociative Br 2 ( Π u 1 ) state Two-photon dissociation and ionization of liquid water studied by femtosecond transient absorption spectroscopyThe ultrafast dissociation of gas-phase Br 2 is probed via a 400 nm pump soft-x-ray probe scheme at five different high-order harmonic wavelengths ͑13th, 15th, 17th, 19th, and 21st of an 800 nm Ti:sapphire laser͒. A series of time-resolved ultrafast photoelectron spectra reveals prompt two-photon ionization features, which allow in situ measurement of the cross correlation between the pump and probe pulses. Transient features are attributed to ionization of the dissociative excited state wave packet, and new spectral peaks are associated with the formation of atomic Br. Deconvolution of time-trace plots of the atomic signals with the cross-correlation pulse durations reveal similar dissociation times ͑ϳ40 fs͒ at two probe wavelengths ͑47 and 42 nm͒. Analysis of the transient wave packet photoelectron signal suggests an ionization process that occurs during dissociation, with a broad electron kinetic energy distribution at an extended Br-Br bond length ͑R у3 Å͒. At long delay times ͑у500 fs͒, an enhancement of the ionization cross section of the Br atom compared to the Br 2 molecule is observed with each of the probe wavelengths, the ratio increasing from a factor of 21Ϯ1 to 56Ϯ5 for probe wavelengths of 61.5 to 38 nm, respectively. The intensity of the transient wave packet signal on the dissociative state remains nearly constant between the 17th and 19th harmonic probes, indicating that the ionization cross section of the dissociative state has an entirely different wavelength dependence than the Br atom. The transient wave packet ionization signal is qualitatively 10%-20% of the simultaneous two-photon ͑400 nmϩsoft x-ray͒ ionization signal. The results are discussed in terms of the transient dynamics of dissociative state photoelectron spectroscopy, the correlation between molecular and atomic ionization probabilities, and above threshold ionization probabilities.
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