scholarly journals Nonlinear two-dimensional terahertz photon echo and rotational spectroscopy in the gas phase

2016 ◽  
Vol 113 (42) ◽  
pp. 11800-11805 ◽  
Author(s):  
Jian Lu ◽  
Yaqing Zhang ◽  
Harold Y. Hwang ◽  
Benjamin K. Ofori-Okai ◽  
Sharly Fleischer ◽  
...  
Keyword(s):  
Gas Phase ◽  
Degrees Of Freedom ◽  
Terahertz Spectroscopy ◽  
Electromagnetic Spectrum ◽  
Dynamic Features ◽  
Dipole Orientation ◽  
Rotational Spectra ◽  
Dipole Interactions ◽  
Linear Spectrum ◽  
Rotational Coupling

Ultrafast 2D spectroscopy uses correlated multiple light−matter interactions for retrieving dynamic features that may otherwise be hidden under the linear spectrum; its extension to the terahertz regime of the electromagnetic spectrum, where a rich variety of material degrees of freedom reside, remains an experimental challenge. We report a demonstration of ultrafast 2D terahertz spectroscopy of gas-phase molecular rotors at room temperature. Using time-delayed terahertz pulse pairs, we observe photon echoes and other nonlinear signals resulting from molecular dipole orientation induced by multiple terahertz field−dipole interactions. The nonlinear time domain orientation signals are mapped into the frequency domain in 2D rotational spectra that reveal J-state-resolved nonlinear rotational dynamics. The approach enables direct observation of correlated rotational transitions and may reveal rotational coupling and relaxation pathways in the ground electronic and vibrational state.

scholarly journals Nuclear phase transition and thermodynamic instabilities in dense nuclear matter

2018 ◽  
Vol 182 ◽  
pp. 03007
Author(s):  
A. Lavagno
Keyword(s):  
Phase Transition ◽  
Nuclear Matter ◽  
Gas Phase ◽  
Degrees Of Freedom ◽  
Baryon Density ◽  
Hadronic Matter ◽  
Mechanical Instability ◽  
Dense Nuclear Matter ◽  
Nuclear Phase ◽  
Matter Phase

We study the presence of thermodynamic instabilities in a nuclear medium at finite temperature and density where nuclear phase transitions can take place. Such a phase transition is characterized by pure hadronic matter with both mechanical instability (fluctuations on the baryon density) that by chemical-diffusive instability (fluctuations on the electric charge concentration). Similarly to the liquid-gas phase transition, the nucleonic and the Δ-matter phase have a different isospin density in the mixed phase. In the liquid-gas phase transition, the process of producing a larger neutron excess in the gas phase is referred to as isospin fractionation. A similar effects can occur in the nucleon-Δ matter phase transition due essentially to a Δ- excess in the Δ-matter phase in asymmetric nuclear matter. In this context we also discuss the relevance of Δ-isobar and hyperon degrees of freedom in the bulk properties of the protoneutron stars at fixed entropy per baryon, in the presence and in the absence of trapped neutrinos.

Impact of photochemical hazes on the thermal structure of exoplanet atmospheres

2020 ◽  
Author(s):  
Panayotis Lavvas ◽  
Anthony Arfaux
Keyword(s):  
Chemical Composition ◽  
Gas Phase ◽  
Thermal Structure ◽  
Temperature Inversion ◽  
Upper Atmosphere ◽  
Lower Atmosphere ◽  
Cloud Formation ◽  
Electromagnetic Spectrum ◽  
Heating Efficiency ◽  
The Impact

<p>Transit observations reveal that a significant population of the detected exoplanets has hazy atmospheres (Sing et al. 2016). Although the relative contribution of clouds and photochemical aerosols is not yet fully clarified, the impact of haze particles on the thermal structure could be significant, as such particles can efficiently scatter and absorb radiation over a large part of the electromagnetic spectrum. Particularly, photochemical aerosols are anticipated to be present at pressures lower than those of cloud formation. The transit observations of HD 189733 b indicate that the haze opacity responsible for the UV-Visible slope is located at pressures between 1μbar and 1 mbar. As such low pressures, the presence of hazes could allow for strong temperature inversions due to the low atmospheric density. We investigate here the implications of such hazes on the exoplanet atmospheric thermal structure.</p> <p>We simulate the atmospheric thermal structure using a 1D radiative-convective model. The model utilizes non-equilibrium chemical composition results (Lavvas et al. 2014) for the gas phase composition, and haze particle size distributions calculated from an aerosol microphysical growth model (Lavvas & Koskinen 2017, Lavvas et al. 2019). We do not yet consider the non-LTE effects for the gases, but we do take into account the impact of temperature disequilibrium between the particles and the gas envelope that can strongly affect the heating efficiency of the particles. We consider various gas phase opacities from atomic and molecular contributions calculated through correlated-k coefficients.</p> <p>Our results demonstrate that in the lower atmosphere the simulated temperature profiles provide emission spectra that are in good agreement with the eclipse observations for the simulated targets (HD 209458 b and HD 189733 b). In the upper atmosphere of the hazy HD 189733 b the simulated haze distribution, which fits the transit observations, results in a strong temperature inversion. On the contrary, the upper atmosphere of the clear HD 209458 b, is significantly colder compared to previous evaluations based on equilibrium chemistry assumption. The implications of these results on the chemical composition will be discussed, as well as results from other exoplanet cases.</p> <p> </p>

scholarly journals Rotational action spectroscopy of trapped molecular ions

2021 ◽  
Author(s):  
Oskar Asvany ◽  
Stephan Schlemmer
Keyword(s):  
Experimental Method ◽  
Molecular Ions ◽  
Electromagnetic Spectrum ◽  
Action Spectroscopy ◽  
Rotational Spectra

Rotational action spectroscopy is an experimental method in which rotational spectra of molecules, typically in the microwave to sub-mm-wave domain of the electromagnetic spectrum (∼ 1-1000 GHz), are recorded by...

scholarly journals The quest of chirality in the interstellar medium

2020 ◽  
Vol 633 ◽  
pp. A49
Author(s):  
Y. Ellinger ◽  
F. Pauzat ◽  
A. Markovits ◽  
A. Allaire ◽  
J.-C. Guillemin
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
Propylene Oxide ◽  
Density Functional ◽  
Energy Scale ◽  
Potential Candidate ◽  
Structural Constraints ◽  
Water Ice ◽  
Rotational Spectra ◽  
Complex Organic Molecule

Context. All but one complex organic molecule (COM) detected so far in the interstellar medium (ISM) are achiral; propylene oxide (c-C2H3O)-CH3 is the only exception to this. Finding other chiral species is a priority for astrobiology to progress in the understanding of the emergence of life. Whatever the conditions of their formation, i.e., gas phase or grain chemistry, the detection relies on rotational spectra. This means that, if adsorbed after formation in the gas phase or directly formed on the icy grains, these COMs must escape in the gas phase as free flyers to be detectable. Aims. Learning the lesson drawn from the only observation of a chiral compound and considering the structural constraints imposed to a molecule to be chiral, we look at what species could satisfy these conditions and be potential targets for a radio astronomy search in the ISM gas phase. Methods. This question was addressed by combining two complementary approaches that rely on density functional theory. The structure, energetics, and spectroscopic parameters of each potential candidate were determined using molecular calculations. The propensity for a molecule to remain trapped on the ice coating of the grains was evaluated by numerical simulations making use of a solid state periodic model. Results. Replacing the -CH3 group on rigid propylene oxide by -CN, -CCH, -NH2, -OH, or -HCO gives oxirane daughter molecules whose adsorption energies divide into two classes: below and above the adsorption energy of H2O on solid water-ice ~13.5 kcal mol−1. Conclusions. The best chiral candidate would be a rigid molecule for an easier determination of its radio spectra. This molecule would be composed of a central carbon linked to one hydrogen and three different chemical groups as simple as possible. If not the most stable isomer, this candidate should be as close as possible on the energy scale, possess a significant dipole moment, and be less strongly attached to the ice than H2O itself.

Acetyl Cyanide II. Rotation–Torsion–Vibration Interaction in the Rotational Spectrum

1976 ◽  
Vol 31 (11) ◽  
pp. 1398-1407 ◽  
Author(s):  
F. Scappini ◽  
H. Mäder ◽  
H. Dreizler
Keyword(s):  
Excited States ◽  
Ground State ◽  
Degrees Of Freedom ◽  
Rotational Spectrum ◽  
Rotational Spectra ◽  
Torsion Vibration ◽  
First Excited State ◽  
Methyl Torsion ◽  
Theoretical Considerations ◽  
Internal Degrees Of Freedom

Abstract The rotation-torsion-vibration interaction in acetyl cyanide, CH3COCN, has been studied in the rotational spectra of the first excited state of the methyl torsion and of the CCN-in-plane bending. A model with two internal degrees of freedom has been used to account for the A-E rotational splittings in the ground state and in the two excited states simultaneously. The constants in the Fourier expansion of the potential hindering the methyl torsion are determined. The results are compared with those obtained in a previous work from the A-E rotational splittings of the ground state only, using a model with one degree of freedom. Group theoretical considerations are made upon the Hamiltonian used in the present analysis.

Eine Analyse der Methyltorsionsfeinstruktur von Rotationsspektren in angeregten Zuständen der S-S-Torsion beim Trideutero-methyl-methyldisulfid / An Analysis of Methyltorsion Finestructure in Rotational Spectra of Excited States of S-S-Torsion of Trideutero-methyl-methyldisulfide

1974 ◽  
Vol 29 (9) ◽  
pp. 1335-1344 ◽  
Author(s):  
M. Kuhler ◽  
L. Charpentier ◽  
D. Sutter ◽  
H. Dreizier
Keyword(s):  
Fine Structure ◽  
Excited States ◽  
Degrees Of Freedom ◽  
Microwave Spectrum ◽  
Eine Analyse ◽  
Rotational Spectra ◽  
Methyl Torsion ◽  
Internal Degrees Of Freedom

The microwave spectrum of CH3SS CD3 was investigated in the range of 5 -40 GHz. Rotational spectra in different states of the S-S-torsion were assigned. The methyl torsion fine structure of these spectra was measured and compared with calculations based on a Hamiltonian formulated for a model with two internal degrees of freedom, the methyl and S-S-torsion.

The gas-phase infrared spectra of nitromethane and methyl boron difluoride; fine structure caused by internal rotation

1968 ◽  
Vol 304 (1477) ◽  
pp. 135-155 ◽  
Keyword(s):  
Fine Structure ◽  
Gas Phase ◽  
Internal Rotation ◽  
Infrared Spectra ◽  
Degrees Of Freedom ◽  
Coupling Constants ◽  
Modes Of Vibration ◽  
Simplifying Assumptions ◽  
Boron Difluoride ◽  
Vibration Rotation

The gas-phase infrared spectra of nitromethane and methyl boron difluoride have been analysed in some detail. The various skeletal modes of vibration, and the vibrations of the methyl group with dipole changes parallel to the carbon–nitrogen and carbon–boron axes respectively, have vibration–rotation band contours which are of the expected type as calculated from the moments of inertia for overall rotation of the molecules. The perpendicular vibrations of the methyl groups all have complex contours, and in a number of cases widely-spaced fine structure lines are present. These can only be accounted for in terms of the internal rotation degrees of freedom. This is as expected because in classical terms the internal rotation frequencies modulate the oscillating vibrational dipole moment of these (and only these) methyl vibrations; in quantum-mechanical terms this leads to addi­tional transitions involving changes in the quantum number for internal rotation. These perpendicular methyl vibration bands have complex rotational structure because of interaction of the internal rotation degree of freedom with the overall rotations of these asymmetric top molecules. Nevertheless their main Q -branch features have been rather successfully analysed in terms of a theoretical model in which it is assumed that the internal rotation is free, and that the degeneracies of these perpendicular modes are retained. The former is expected to be a good approximation because of the known very low barriers to internal rotation. Some unresolved complexities, particularly towards the centres of the bands, may be caused by deviations from these simplifying assumptions. Analyses of the bands in this manner leads to information about the band origins and to reasonable values for the Coriolis coupling constants of the degenerate vibrations.

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