Actively phase-locked heterodyne-detected fifth-order nonresonant Raman scattering from room temperature CS2 has been measured. The experimental signals have similar magnitudes, shapes, and sign changes as calculated responses obtained via molecular dynamics simulations [S. Saito and I. Ohmine, Phys. Rev. Lett. 88, 207401 (2002)]. The measured signals contain sign changes that appear to be associated with the coupling of rotational motions both to each other and to translational motions.

Resonance Raman spectra of the simple peptide model compound IV-methylacetamide have been obtained with 218-and 200-nm laser radiation. A large enhancement of the amide II vibration is observed relative to that of Raman spectra obtained with visible radiation. Replacement of the amide hydrogen by deuterium results in a spectrum with most of its intensity in the amide II' mode. Excitation of this deuterated species with 200-nm radiation results in intensity in the overtones of this modes, a feature characteristic of resonance enhanced spectra. Isotopic substitution of the amide carbon and nitrogen by 13C and 15N results in a spectral shift to lower frequency by nearly the amount expected for a normal mode consisting primarily of the motion of the amide C and N atoms. These results, taken together, demonstrate that the geometry change of IV-methylacetamide upon electronic excitation to the v-ir* state is dominated by a change in the C-N bond length. Studies of mixtures of the deuterio and protio forms show that a significant normal mode rotation occurs on isotopic substitution such that the amide II' of the deuterio form becomes approximately equally distributed between the amide II and III vibrations of the protio form. The amide I and I' vibrations are very diffuse in aqueous solutions at the high dilutions used. These bands become sharp in acetonitrile. This behavior to a distribution of hydrogen-bonded species.

We show that ultra-cold atoms with synthetic spin-orbit coupling in Raman lattices can be used as versatile quantum simulators to explore the connections between correlated Chern insulators and strongly-coupled four-Fermi field theories related to the Gross-Neveu model in (2+1) dimensions. Exploiting this multidisciplinary perspective, we identify a large-N quantum anomalous Hall (QAH) effect in absence of any external magnetic field, and use it to delimit regions in parameter space where these correlated topological phases appear, the boundaries of which are controlled by strongly-coupled fixed points of the four-Fermi relativistic field theory. We further show how, for strong interactions, the QAH effect gives way to magnetic phases described by a two-dimensional quantum compass model in a transverse field. We present a detailed description of the phase diagram using the large-N effective potential, and variational techniques such as projected entangled pairs.

The depolarized reduced Raman and corresponding optical Kerr effect (OKE) spectral density of ambient CS2 have been calculated by way of time correlation function (TCF) and instantaneous normal mode (INM) methods and compared with experimental OKE data. When compared in the reduced Raman spectrum form, where the INM spectrum is proportional to the squared polarizability derivative weighted density of states (DOS), the INM results agree nearly quantitatively (at all but the lowest frequencies) with the TCF results. Both are in excellent agreement with experimental measurements. The INM signal has a significant contribution from the imaginary INMs. Within our INM theory of spectroscopy the imaginary INMs contribute like the real modes, at the magnitude of their imaginary frequency. When only the real modes are allowed to contribute, and the spectrum is rescaled to account for the missing degrees of freedom, the results are much poorer, as has been observed previously. When the spectra are compared in their OKE form, the INM spectrum is found to lack the low-frequency spike which is associated with long time scale rotational diffusion, and it is not surprising that an INM theory would not capture such a feature. The results demonstrate that while the OKE and spontaneous depolarized Raman spectrum contain the same information, they clearly highlight different dynamical time scales. At higher frequencies (ω>25 cm−1) the INM OKE results are in excellent agreement with TCF and experimental results. The TCF results capture the low-frequency spike and are in agreement with experiment everywhere within the precision of the present calculations. The molecular contributions to the OKE signal are analyzed using INM methods.