The stiffness of a fully stretched polyethylene chain: A Raman jet spectroscopy extrapolation

Tobias N. Wassermann, Jonas Thelemann, Philipp Zielke, and Martin A. Suhm

The elastic modulus of an isolated polyethylene chain in vacuum is determined by extrapolation of the LAMs of n-alkanes with 7–16 C-atoms to infinity. It has a value of 309±8 GPa, orders of magnitude larger than measured for most real stretched polymer samples and still significantly larger than estimated by x-ray crystallography.

J. Chem. Phys. 131, 161108 (2009)

Observation of buried water molecules in phospholipid membranes by surface sum-frequency generation spectroscopy

Maria Sovago, Erik Vartiainen, and Mischa Bonn

The structure and orientation of water molecules at the water-lipid interface, using vibrational sum-frequency generation in conjunction with a maximum entropy phase retrieval method are investigated. It is found that interfacial water molecules have an orientation opposite to that predicted by electrostatics and thus are likely localized between the lipid headgroup and its apolar alkyl chain. This type of water molecule is observed for phospholipids but not for structurally simpler surfactants.

J. Chem. Phys. 131, 161107 (2009)

Direct visualization of the H–Xe bond in xenon hydrides: Xenon isotopic shift in the IR spectra

Vladimir I. Feldman, Alexey V. Kobzarenko, Irina A. Baranova, Alexander V. Danchenko, Fedor F. Sukhov, Ehud Tsivion, and R. Benny Gerber

IR spectra of xenon hydrides (HXeCCH, HXeCC, and HXeH) obtained from different xenon isotopes (¹²⁹Xe and ¹³⁶Xe) exhibit a small but detectable and reproducible isotopic shift in the absorptions assigned to H–Xe stretching (by 0.17–0.38  cm−1). To our knowledge, it is the first direct experimental evidence for the H–Xe bond in HXeY type compounds. The shift magnitude is in good agreement with quantum-chemical calculations.

J. Chem. Phys. 131, 151101 (2009)

Three-dimensional electronic spectroscopy of excitons in GaAs quantum wells

Daniel B. Turner, Katherine W. Stone, Kenan Gundogdu, and Keith A. Nelson

Three-dimensional (3D) electronic Fourier transform spectroscopy of GaAs quantum wells using four fully phase-coherent, noncollinear optical fields is demonstrated.  The full complex signal field is measured as a function of all three time intervals, leading to nearly every peak in the resulting 3D spectral solid arising from a distinguishable sequence of transitions represented by a single Feynman pathway. The 3D spectral peaks are used to separate two pathways involving weakly bound mixed biexcitons generated in different time orders. In the process, a peak that was previously obscured by a correlated but unbound exciton pair coherence is revealed.

J. Chem. Phys. 131, 144510 (2009) | Physics Update