Biomedical subjects

R E Continetti

Publications and source records attributed to R E Continetti.

4 recordsLinked to original sources

PubMed2001

Effects of alkyl substitution on the energetics of enolate anions and radicals.

The photoelectron spectra of the structural isomers of the three- and four-carbon enolate anions, n-C3H5O(-), i-C3H5O(-), n-C4H7O(-), s-C4H7O(-), and i-C4H7O(-) have been measured at 355 nm. Both the X(2A' ') ground and A(2A') first excited states of the corresponding radicals were accessed from the X(1A') ground state of the enolate anions. The separation energies of the ground and first excited states (T0) were determined: T0[(E)-n-C3H5O] = 1.19 +/- 0.02 eV, T0[(Z)-n-C3H5O] = 0.99 +/- 0.02 eV, T0[i-C3H5O] = 1.01 +/- 0.02 eV, T0[n-C4H7O] = 1.19 +/- 0.02 eV, T0[(2,3)-s-C4H7O] = 1.25 +/- 0.02 eV, T0[(1,2)-s-C4H7O] = 0.98 +/- 0.02 eV, and T0[i-C4H7O] = 1.36 +/- 0.02 eV. The effects of alkyl substitution on the vibronic structure and energetics previously observed in the vinoxy radical are discussed. The X(1A')-X(2A' ') relative stability is strongly influenced by substitution whereas the X(1A')-A(2A') relative stability remains nearly constant for all of the observed structural isomers. Alkyl substitution at the carbonyl carbon affects vibronic structure more profoundly than the energetics, while the converse is observed upon alkyl substitution at the alpha carbon.

Journal Article↗

PubMed2001

Coincidence spectroscopy.

The application of coincidence techniques to the study of the reaction dynamics of isolated molecules is reviewed. Coincidence spectroscopy is a powerful approach for carrying out a number of measurements. At its most basic level, coincidence techniques can identify the source of a specific signal, as in the well-known photoelectron-photoion coincidence approach used for several years. By carrying out coincidence experiments in an increasingly differential manner, correlated energy and angular distributions of reaction products may be recorded. Completely energy- and angle-resolved measurements of photoelectrons and ionic or neutral products can reveal molecular-frame photoelectron and photofragment angular distributions and aid in the characterization of dissociative states of molecules and ions. Recent work in this area is reviewed, including examples from studies of dissociative photodetachment, dissociative photoionization, time-resolved studies of dissociative photoionization, and three-body dissociation processes.

Journal Article↗

PubMed2000

Femtosecond time-resolved photoelectron angular distributions probed during photodissociation of NO2.

Femtosecond time-resolved photoelectron angular distributions (PADs) are measured for the first time in the molecular frame of a dissociating molecule. Various stages of the dissociation process, NO2-->NO(C Pi)+O(P), are probed using ionization of the NO(C Pi) fragment to NO+(X Sigma(+)). The PADs evolve from forward-backward asymmetric with respect to the dissociation axis at short time delays ( < or =500 fs) to symmetric at long time delays (> or = 1 ps). Changes in the PADs directly reflect the time-dependent separation and reorientation of the dissociating photofragments.

Journal Article↗

PubMed2000

Transition state dynamics of the OH + H2O hydrogen exchange reaction studied by dissociative photodetachment of H3O2-.

Dynamics in the transition state region of the bimolecular OH + H2O-->H2O + OH hydrogen exchange reaction have been studied by photoelectron-photofragment coincidence spectroscopy of the H3O2- negative ion and its deuterated analog D3O2-. The data reveal vibrationally resolved product translational energy distributions. The total translational energy distribution shows a vibrational progression indicating excitation of the antisymmetric stretch of the water product. Electronic structure calculations at the QCISD level of theory support this analysis. Examination of the translational energy release between the neutral products reveals a dependence on the product vibrational state. These data should provide a critical test of ab initio potential energy surfaces and dynamics calculations.

Hydroxides↗