A master equation approach to the dynamics of zero electron kinetic energy (ZEKE) states and ZEKE spectroscopy.

We have theoretically studied important dynamic processes involved in zero electron kinetic energy (ZEKE) spectroscopy using the density matrix method with the inverse Born-Oppenheimer approximation basis sets. In ZEKE spectroscopy, the ZEKE Rydberg states are populated by laser excitation (either a one- or two-photon process), which is followed by autoionizations and l-mixing due to a stray field. The discrimination field is then applied to ionize loosely bound electrons in the ZEKE states. This is followed by using the extraction field to extract electrons from the ZEKE levels which have a strength comparable to that of the extraction field. These extracted electrons are measured for the relative intensities of the ion states under investigation. The spectral positions are determined by the applied laser wavelength and modified by the extraction electric field. In this paper, all of these processes are conducted within the context of the density matrix method. The density matrix method can provide not only the dynamics of system's population and coherence (or phase) but also the rate constants of the processes involved in the ZEKE spectroscopy. Numerical examples are given to demonstrate the theoretical treatments.

Experimental and theoretical investigations of ionization/dissociation of cyclopentanone molecule in a femtosecond laser field.

The ionization/dissociation mechanism of cyclopentanone has been experimentally investigated in molecular beam by irradiating with intense 394 and 788 nm laser fields with pulse duration of 90 fs. The range of laser intensities varied from 3 x 10(13) to 4 x 10(14) W/cm(2). For both wavelengths, the singly charged parent ion is observable while the doubly charged one cannot be found easily, although the fragmentation pattern supports its presence. Meanwhile, the extent of fragmentation at 788 nm is less than that in the 394 nm case. We quantitatively analyze the ionization processes of cyclopentanone in intense femtosecond laser by comparing the calculation results of ionization rate constants obtained from Ammosov-Delone-Krainov, Keldysh, and Keldysh-Faisal-Reiss (KFR) theories based on hydrogenlike atom model. We also compare the experimental and theoretical results; the generalized KFR theory is found to be useful in predicting the ionization yields of singly and doubly charged cyclopentanone ion. To interpret the dissociation patterns of the cyclopentanone ions, we have used the Rice-Ramsperger-Kassel-Marcus theory with the potential surfaces obtained from the ab initio quantum chemical calculations.

Catalytic nucleophilic acyl substitution of anhydrides by amphoteric vanadyl triflate.

[reaction--see text] Among four vanadyl species examined, vanadyl triflate was the most efficient catalyst to facilitate nucleophilic acyl substitution of anhydrides with a myriad array of alcohols, amines, and thiols in high yields and high chemoselectivity. By using mixed-anhydride technique, one can achieve oleate and peptide syntheses. In marked contrast to common metal triflates, the amphoteric character of the V=O unit in vanadyl species was proven to be responsible for the catalytic profile in this process.

Short waitlist time does not adversely impact outcome following liver transplantation for hepatocellular carcinoma.

It has been suggested that patients with hepatocellular carcinoma (HCC) undergoing living donor liver transplantation (LDLT) have worse recurrence-free survival compared to deceased donor liver transplantation (CLT), leading to the hypothesis that short waitlist time or fast-tracking may include more aggressive tumors that would have been selected out by traditionally longer waitlist time. The primary aim of the present study was to evaluate the impact of waitlist time on HCC recurrence. The study cohort included 100 patients meeting T2 criteria by imaging before undergoing CLT (n = 90) or LDLT (n = 10). The 5-year recurrence-free probability was 89.9% for the entire cohort, and 91.9%, 90.5% and 86.6%, respectively, for waitlist time of 3 months or less, 3-6 months and > 6 months (p = 0.81). In the Cox proportional hazards model, waitlist time was also not a significant predictor of HCC recurrence. Tumor under-staging was observed in 20.5% of patients with waitlist time 3 months or less and 23.0% for waitlist time > 3 months (p = 0.81). In conclusion, our results failed to show an association between waitlist time and outcome after CLT or LDLT for HCC, and provided evidence disputing a significant role of waitlist time in the selection against HCC with unfavorable tumor biology.

Experimental and theoretical investigation of high-power laser ionization and dissociation of methane.

The main purpose of this paper is to report the high-power laser ionization-dissociation of CH(4) at various femtosecond (fs) laser intensities (from 1 x 10(14) W/cm(2) to 2 x 10(15) W/cm(2)) with a laser pulse duration of 48 fs. The generalized molecular Keldysh theory has been applied to calculate the ionization yields for CH(4)+ and CH(4)++. Outside the influence of the fs intense laser, we propose to calculate the mass spectra due to the decomposition of CH(4)+ and CH(4)++, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The agreement between the experimental mass spectra and calculated mass spectra seems to be reasonable.