All-optical retrieval of the global phase for two-dimensional Fourier-transform spectroscopy

A combination of spatial interference patterns and spectral interferometry are used to find the global phase for non-collinear two-dimensional Fourier-transform (2DFT) spectra. Results are compared with those using the spectrally resolved transient absorption (STRA) method to find the global phase when excitation is with co-linear polarization. Additionally cross-linear polarized 2DFT spectra are correctly phased using the all-optical technique, where the SRTA is not applicable.Comment: 6 pages, 7 figures, journal publicatio

Two-Dimensional Infrared Spectroscopy of Antiparallel β-Sheet Secondary Structure

We investigate the sensitivity of femtosecond Fourier transform two-dimensional infrared spectroscopy to protein secondary structure with a study of antiparallel β-sheets. The results show that 2D IR spectroscopy is more sensitive to structural differences between proteins than traditional infrared spectroscopy, providing an observable that allows comparison to quantitative models of protein vibrational spectroscopy. 2D IR correlation spectra of the amide I region of poly-L-lysine, concanavalin A, ribonuclease A, and lysozyme show cross-peaks between the IR-active transitions that are characteristic of amide I couplings for polypeptides in antiparallel hydrogen-bonding registry. For poly-L-lysine, the 2D IR spectrum contains the eight-peak structure expected for two dominant vibrations of an extended, ordered antiparallel β-sheet. In the proteins with antiparallel β-sheets, interference effects between the diagonal and cross-peaks arising from the sheets, combined with diagonally elongated resonances from additional amide transitions, lead to a characteristic “Z”-shaped pattern for the amide I region in the 2D IR spectrum. We discuss in detail how the number of strands in the sheet, the local configurational disorder in the sheet, the delocalization of the vibrational excitation, and the angle between transition dipole moments affect the position, splitting, amplitude, and line shape of the cross-peaks and diagonal peaks.

Multiple-Point and Multiple-Time Correlations Functions in a Hard-Sphere Fluid

A recent mode coupling theory of higher-order correlation functions is tested on a simple hard-sphere fluid system at intermediate densities. Multi-point and multi-time correlation functions of the densities of conserved variables are calculated in the hydrodynamic limit and compared to results obtained from event-based molecular dynamics simulations. It is demonstrated that the mode coupling theory results are in excellent agreement with the simulation results provided that dissipative couplings are included in the vertices appearing in the theory. In contrast, simplified mode coupling theories in which the densities obey Gaussian statistics neglect important contributions to both the multi-point and multi-time correlation functions on all time scales.Comment: Second one in a sequence of two (in the first, the formalism was developed). 12 pages REVTeX. 5 figures (eps). Submitted to Phys.Rev.

Phenomena of g-u symmetry-breakdown in HD

Phenomena associated with the breakdown of inversion symmetry in the HD molecule are reviewed and discussed. A distinction is made between three kinds of physical effects observed in HD spectra. The existence of a small electric dipole moment in the ground state gives rise to vibrational and pure rotational transitions following selection rules of electric dipole transitions. Coupling between electronic states of g and u symmetry occurs, which is associated with the appearance of forbidden lines in the electronic spectrum. This effect occurs predominantly at near coincidences between levels of opposite inversion symmetry and a recently observed example of strongly interacting states (H̄ ′

MICROWAVE TRANSITIONS IN Na3Na_{3} DETECTED BY RESONANT TWO-PHOTON IONIZATION

Author Institution: Departments of Physics and Chemistry, Penn State University; Frances Bitter Magnet Laboratory, Penn State UniversityThe direct measurement of hyperfine and fine structure as well as tunneling splittings in small clusters can provide information on the localization of electrons and an electron-nuclear coupling mechanism. The ground state of the sodium trimer is split by Jahn-Teller interaction. Energy minima of the potential surface for the nuclei are found corresponding to an isosceles triangle geometry with 80 degree apex angle. The Jahn-Teller distortion gives rise to a small electric dipole moment. Using our new resonant two-photon ionization detection scheme for the absorption of microwaves, we measured rotational transitions in the 12 to 17 GHz region. From intensity measurements, an extremely small electric dipole moment on the order of 0.01 D can be concluded. The detection scheme involves as intermediate steps the optical excitation into various excited electronic states for which the symmetries of rotational levels had previously been assigned. Through careful studies of several rotational states, we found that in some ground state levels, the tunneling splitting is so small that hyperfine mixing forbids any clear assignment of A and E symmetries. In the paper which follows this presentation, Laurent Coudert will introduce an effective hyperfine Hamiltonian taking these effects into account

JAHN-TELLER AND PSEUDO JAHN-TELLER INTERACTIONS IN THE B STATE MANIFOLD OF THE SODIUM TRIMER

$^{a}$ N. Ohashi, M. Tsuura, J.T. Hougen, W.E. Ernst and S. Rakowsky, J. Mol. Spectrosc. 184, 22-34 (1997). $^{b}$ F. Cocchini, T.H. Upton and W. Andreoni. J. Chem. Phys., Vol. 88, No. 10, 6068-6077 (1988). $^{c}$ R. Meiswinkel and H. K\""{o}ppel, Chem. Phys. 144, 117-128 (1990).Author Institution: Department of Physics and Chemistry, The Pennsylvania State UniversityThe B state of $Na_{3}$ is the result of the vibronic coupling of a $^{2}E'$ and a $^{2}A'_{1}$ state. The three states mix by pseudo Jahn-Teller (PJT) and Jahn-Teller (JT) interactions giving rise to three potential surfaces the lowest of which allows for free pseudorotational motion of the Na nuclei. Energy levels in the corresponding lowest vibronic states are well described by a new model $Hamiltonian^{a}$ which includes rotation and pseudorotation. In this talk, we link experimentally determined molecular parameters from the Ohashi-Hougen Hamiltonian to the potential surface picture used by molecular dynamics $theorists^{b,c}$. Of particular interest is the potential barrier to the pseudorotation which lies well below the lowest vibronic state. This small barrier can be caused by PJT or JT interaction or by a combination of both. The Hamiltonian parameter corresponding to the effective barrier height has been well determined from our analysis of high resolution spectra. Measured barrier parameters for different vibronic states allow to distinguish the influences of JT and PJT coupling on the shape of the barrier. Our study suggests that the lowest potential surface is dominated by linear PJT interaction with some smaller amount of quadratic PJT and linear JT coupling

GLOBAL FIT OF THE B-X SYSTEM OF Na3Na_{3} USING A NEW MODEL HAMILTONIAN

Author Institution: Department of Physics, The Pennsylvania State UniversityThe A and X states $Na_{3}$ can be thought of as ordinary asymmetric rotors (complicated slightly by spinrotation interaction) but the B state must be treated as a floppy molecule since it exhibits an almost free pseudorotational $motion^{1,2}$. Because of the peculiar nature of the centrifugal distortion in the B state, previous fitting of the B-X system has been most successful for P and R type transitions involving ground state levels characterized by $J, K_{a}, K_{a} = J, 0, J$ or J, 1, J-1, i.e., levels with $J-K_{c} = 0$ or 1. The present talk will describe our progress in globally fitting recently $recorded^{3}$ transitions involving levels with $J-K_{c} > 1$ in order to more thoroughly test the correctness of the recently developed model $Hamiltonian^{2}$. In addition, our experiments have revealed an unexpected splitting of each Coriolis component in pseudorotational states with angular momentum quantum number $j\geq{1}$. This small splitting--like the larger Coriolis splitting itself--is approximately proportional to $j^{4}$. We believe it arises from some type of interaction between the electron spin angular momentum and the pseudorotational angular momentum. Our attempts to describe this phenomenon will also be discussed