Search

Infrared spectra and intensities of the ν3band of H2O in Ar−H2O and O2−H2O complexes have been studied by helium nanodroplet spectroscopy. It was found that the H2O molecule rotates almost freely in both the Ar−H2O and O2−H2O complexes. Infrared intensities of the ν3band of H2O in these complexes were equal to that of an isolated H2O molecule within experimental errors. The obtained infrared spectra and infrared intensities were compared with those of the N2−H2O complex in helium droplets, which we recently reported. [ABSTRACT FROM AUTHOR]

Infrared spectra and intensities of the ν3band of H2O in Ar−H2O and O2−H2O complexes have been studied by helium nanodroplet spectroscopy. It was found that the H2O molecule rotates almost freely in both the Ar−H2O and O2−H2O complexes. Infrared intensities of the ν3band of H2O in these complexes were equal to that of an isolated H2O molecule within experimental errors. The obtained infrared spectra and infrared intensities were compared with those of the N2−H2O complex in helium droplets, which we recently reported. [ABSTRACT FROM AUTHOR]

Cells store excess energy in the form of cytoplasmic lipid droplets. At present, it is unclear how different types of fatty acids contribute to the formation of lipid droplets. We describe a compound Raman microscope capable of both high-speed chemical imaging and quantitative spectral analysis on the same platform. We used a picosecond laser source to perform coherent Raman scattering imaging of a biological sample and confocal Raman spectral analysis at points of interest. The potential of the compound Raman microscope was evaluated on lipid bodies of cultured cells and live animals. Our data indicate that the in vivo fat contains much more unsaturated fatty acids (FAs) than the fat formed via de novo synthesis in 3T3-L1 cells. Furthermore, in vivo analysis of subcutaneous adipocytes and glands revealed a dramatic difference not only in the unsaturation level but also in the thermodynamic state of FAs inside their lipid bodies. Additionally, the compound Raman microscope allows tracking of the cellular uptake of a specific fatty acid and its abundance in nascent cytoplasmic lipid droplets. The high-speed vibrational imaging and spectral analysis capability renders compound Raman microscopy an indispensible analytical tool for the study of lipid-droplet biology. [ABSTRACT FROM AUTHOR]

We detail the development of an optical probe technique based on time-resolved Raman-induced Kerr effect polarization spectroscopy (tr-RIKES). This technique, termed fs/ps RIKES, combines an ultrafast pump pulse with a narrowband probe that directly allows spectral resolution of low-frequency (0−600 cm−1) modes typically observable via RIKES. The narrowband probe pulse alleviates the need to scan the time delay between pump and probe pulses to observe molecular coherences, thus making this multiplexed technique a convenient probe for studying low-frequency molecular dynamics. An important distinguishing characteristic of this polarization-sensitive technique arises from the fact that the delay between the impulsive pump pulse and the picosecond-duration probe pulse is optimized to maximize suppression of nonresonant background signal. Model systems, including the rotational spectrum of gas-phase hydrogen and the low-frequency vibrational spectrum of neat bromoform, are used to compare fs/ps RIKES with the conventional time-resolved RIKES technique. [ABSTRACT FROM AUTHOR]

Infrared spectra of the NH stretching vibrations of (NH3)nclusters (n2−4) have been obtained using the helium droplet isolation technique and first principles electronic structure anharmonic calculations. The measured spectra exhibit well-resolved bands, which have been assigned to the 1, 3, and 24modes of the ammonia fragments in the clusters. The formation of a hydrogen bond in ammonia dimers leads to an increase of the infrared intensity by about a factor of 4. In the larger clusters the infrared intensity per hydrogen bond is close to that found in dimers and approaches the value in the NH3crystal. The intensity of the 24overtone band in the trimer and tetramer increases by a factor of 10 relative to that in the monomer and dimer, and is comparable to the intensity of the 1and 3fundamental bands in larger clusters. This indicates the onset of the strong anharmonic coupling of the 24and 1modes in larger clusters. The experimental assignments are compared to the ones obtained from first principles electronic structure anharmonic calculations for the dimer and trimer clusters. The anharmonic calculations were performed at the Møller−Plesset (MP2) level of electronic structure theory and were based on a second-order perturbative evaluation of rovibrational parameters and their effects on the vibrational spectra and average structures. In general, there is excellent (<20 cm-1) agreement between the experimentally measured band origins for the N−H stretching frequencies and the calculated anharmonic vibrational frequencies. However, the calculations were found to overestimate the infrared intensities in clusters by about a factor of 4. [ABSTRACT FROM AUTHOR]