Heterodyne-detected sum frequency generation spectroscopy of polyacrylic acid at the air/water-interface.

The conformational and hydration behavior of polyacrylic acid (PAA) at the air/water interface is studied using heterodyne-detected vibrational sum frequency generation spectroscopy (HD-VSFG). The amount of adsorption at the water-air interface and the influence of PAA on the water structure at the interface are found to be highly dependent on the degree of ionization (acid dissociation) of the carboxylic acid groups. At a low degree of ionization PAA is surface active and remains in a dense packing arrangement with intrachain hydrogen bonds.

Large scale polarizability calculations using the approximate coupled cluster model CC2 and MP2 combined with the resolution-of-the-identity approximation.

We present an implementation of static and frequency-dependent polarizabilities for the approximate coupled cluster singles and doubles model CC2 and static polarizabilities for second-order Mo̸ller-Plesset perturbation theory. Both are combined with the resolution-of-the-identity approximation for electron repulsion integrals to achieve unprecedented low operation counts, input-output, and disc space demands. To avoid the storage of double excitation amplitudes during the calculation of derivatives of density matrices, we employ in addition a numerical Laplace transformation for orbital energy denominators.