Some complex pressure effects on spectra from simple classical mechanics

I will first recall how [the two Newton's equations, 1rst year of university] one can very easily compute the rotational and translational classical dynamics of an ensemble of linear molecules interacting through an (input) pair-wise intermolecular potential. These Classical Molecular Dynamics Simulations (CMDS), which provide the time dependence of the positions and axis-orientations of gas phase molecules, are then used to calculate a number of pressure effects manifesting in absorption and scattering spectra. The cases of CO2, O2 and N2 will be considered, systems for which fully quantum approaches are intractable, and comparisons with measured data will be made, free of any adjusted parameter. I will show that, with a few input ingredients from literature (molecule geometry, electric multipoles, polarizabilities, ...) an no adjusted parameter, excellent agreements with various measurements are obtained. Examples will be given for: (1) Collision induced absorption (due to the interaction induced dipole)(2) The far wings of absorption (due to the dipole) and light scattering (due to polarizability) bands(3) The broadening and shapes (with their deviations from the Voigt profile) of individual absorption lines for both "free" and spatially tightly confined gases. If times allows, additional demonstrations of the interest of CMDS will be given by considering line-mixing effects and the relaxation of laser-kicked molecules

Laser-induced alignment of nanoparticles and macromolecules for single-particle-imaging applications

Laser-induced alignment of particles and molecules was long envisioned to support three-dimensional structure determination using single-particle imaging with x-ray free-electron lasers [PRL 92, 198102 (2004)]. However, geometric alignment of isolated macromolecules has not yet been demonstrated. Using molecular modeling, we analyzed and demonstrated how the alignment of large nanorods and proteins is possible with standard laser technology, and performed a comprehensive analysis on the dependence of the degree of alignment on molecular properties and experimental details. Calculations of the polarizability anisotropy of about 150,000 proteins yielded a skew-normal distribution with a location of 1.2, which reveals that most of these proteins can be aligned using appropriate, realistic experimental parameters. Moreover, we explored the dependence of the degree of alignment on experimental parameters such as particle temperature and laser-pulse energy

The CO2 –broadened H2O continuum in the 100–1500 cm -1 region: Measurements, predictions and empirical model

Transmission spectra of H2O + CO2 mixtures have been recorded, at 296, 325 and 366 K, for various pres- sures and mixture compositions using two experimental setups. Their analysis enables to retrieve values of the “continuum”absorption by the CO2 -broadened H2O line wings between 100 and 1500 cm-1 . The results are in good agreement with those, around 1300 cm-1 , of the single previous experimental study available. Comparisons are also made with direct predictions based on line-shape correction factors χ calculated, almost thirty years ago, using a quasistatic approach and an input H2O –CO2 intermolecular potential. They show that this model quite nicely predicts, with slightly overestimated values, the con- tinuum over a spectral range where it varies by more than three orders of magnitude. An empirical cor- rection is proposed, based on the experimental data, which should be useful for radiative transfer and climate studies in CO2 rich planetary atmospheres

Lattice strain and tilt mapping in stressed Ge microstructures using X-ray Laue micro-diffraction and rainbow-filtering

Micro-Laue diffraction and simultaneous rainbow-filtered micro-diffraction were used to measure accurately the full strain tensor and the lattice orientation distribution at the sub-micron scale in highly strained, suspended Ge micro-devices. A numerical approach to obtain the full strain tensor from the deviatoric strain measurement alone is also demonstrated and used for faster full strain mapping. We performed the measurements in a series of micro-devices under either uniaxial or biaxial stress and found an excellent agreement with numerical simulations. This shows the superior potential of Laue micro-diffraction for the investigation of highly strained micro-devices.Comment: 28 pages, 10 figure

Extended point defects in crystalline materials: Ge and Si

B diffusion measurements are used to probe the basic nature of self-interstitial 'point' defects in Ge. We find two distinct self-interstitial forms - a simple one with low entropy and a complex one with entropy ~30 k at the migration saddle point. The latter dominates diffusion at high temperature. We propose that its structure is similar to that of an amorphous pocket - we name it a 'morph'. Computational modelling suggests that morphs exist in both self-interstitial and vacancy-like forms, and are crucial for diffusion and defect dynamics in Ge, Si and probably many other crystalline solids