Timothy C. Corcoran

Rotational coherence spectroscopy and structure of phenol dimer

Rotational coherence spectroscopy has been used to measure the rotational constants of four isotopomers of phenol dimer and a single isotopomer of p‐cresol dimer. From the results of these measurements, together with spectroscopic results reported by others, a geometry for phenol dimer is deduced. The species is found to be bound by an O–H⋅⋅⋅O hydrogen bond. The orientation of the phenyl moieties is such that they make maximal contact consistent with the constraints imposed by the hydrogen bond and by the van der Waals radii of the atoms. This geometric feature is cited as evidence for the significance of aromatic–aromatic attraction in the intermolecular interaction between the phenols.

Conformational analysis of jet-cooled tryptophan analogs by rotational coherence spectroscopy

Abstract Excited state rotational constants obtained by rotational coherence spectroscopy are reported for different conformers of jet-cooled tryptamine, 3-indole acetic acid, and 3-indole propionic acid. From the measured constants and information from other sources, conclusions about the structures of the conformers are made.

Ground-state rotational coherence spectroscopy of jet-cooled molecules by stimulated Raman-induced fluorescence depletion

Abstract We report the demonstration of a new technique of rotational coherence spectroscopy that applies to the time-domain measurement of ground-state rotational constants. The technique, stimulated Raman-induced fluorescence depletion, is a picosecond pump-probe scheme in which ground-state rotational coherences prepared via stimulated Raman scattering by the pump pulse are probed via fluorescence induced by the vibronically resonant, variably delayed probe pulse. The scheme is demonstrated with experiments on jet-cooled t -stilbene. The potential of the method and its relation to other techniques are discussed.

Fourier transform stimulated emission pumping spectroscopy

Abstract Theoretical and experimental results that demonstrate a new technique of non-linear interferometry based on stimulated emission pumping spectroscopy (SEPS) are presented. It is shown that splittings between the initial and final states in SEP processes can be measured by the method. Advantages and disadvantages of the technique relative to spectral domain SEPS are discussed.

THE EFFECT OF IONIC STRENGTH AND pH ON THE PROTONATED SCHIFF BASE AND TYROSINE DEPROTONATION KINETICS DURING THE BACTERIORHODOPSIN PHOTOCYCLE

Abstract— The deprotonation kinetics of tyrosine and the protonated Schiff base during the bacteriorho‐dopsin photocycle were studied under different perturbations by transient absorption spectroscop Native purple membrane, as well as samples which were deionized (blue) then restored with Na+ or La3+ were used at pHs ranging from 7 to 10 at very low salt concentrations. The results were compared with previous studies at higher ionic strength. The important conclusions can be summarized as follows: (a) The rate constants of both the Schiff base and tyrosine deprotonation are not very sensitive to the changes of conditions. (b) An almost linear relationship is observed between the relative amplitudes of the tyrosine deprotonated during the cycle and the slow component of the Schiff base deprotonation under the different perturbations studied. This was taken to support the two site model for the protonated Schiff base, one near tyrosine and the other near its ionized form. (c) The pKa value determined from the ratio of the amplitude of the fast to the slow component of the Schiff base deprotonation is found to decrease with increasing ionic strength of the medium. At extremely low ionic strength, it was found to equal that of the tyrosine phenolic group in solution.

Down-shifting of high frequency components in non-linear interferometry

Abstract Theoretical and experimental results are presented that demonstrate a scheme by which one can significantly decrease the modulation frequencies that obtain in interferometric versions of non-linear spectroscopies. This “down-shifting” scheme, by reducing dramatically the number of data points needed to characterize a given spectral region at a given resolution, renders feasible high resolution molecular spectroscopic studies that would otherwise be impractical due to data collection time constraints.

Rotational coherence spectroscopy: picosecond techniques applied to high-resolution rotational spectroscopy

This paper pertains to rotational coherence spectroscopy, a time-domain method of high resolution rotational spectroscopy based on the quantum beat phenomenon. We present a brief discussion of the theoretical basis of the method and a consideration of its advantages over spectral domain methods. We also present experimental results on two species - 1,2-diphenyl acetylene and the tryptamine-(methanol) hydrogen-bonded complex - as further examples of the utility of the method in studies of large species.