Verification of the vibrational exciton approach for CO2 and N2O nanoparticles

Signorell, Ruth

doi:10.1063/1.1531622

Cited by 52 publications

(101 citation statements)

References 51 publications

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“…This effect has its molecular origin in strong transition dipole coupling (vibrational exciton coupling). 35,38,39 As we have discussed and verified by modeling in previous publications, 34, 36 the time evolution of these bands is the result of a shape change from cube-like particles to particles with increasingly elongated shapes. The ν 3 band of the cube-like particles features a strong central peak (2361.0 cm −1 ) with a weak, higher energy side peak (2371.2 cm −1 ).…”

Section: A Pure Co 2 and Pure C 2 H 2 Aerosolsmentioning

confidence: 67%

Infrared spectroscopy and modeling of co-crystalline CO2·C2H2 aerosol particles. I. The formation and decomposition of co-crystalline CO2·C2H2 aerosol particles

Preston

Wang

Signorell

2012

The Journal of Chemical Physics

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Aerosol particles composed of co-crystalline CO(2)·C(2)H(2) were generated in a bath gas cooling cell at cryogenic temperatures and investigated with infrared spectroscopy between 600 and 4000 cm(-1). Similar to results obtained for thin films of the co-crystal [T. E. Gough and T. E. Rowat, J. Chem. Phys. 109, 6809 (1998)], this phase was found to be metastable and decomposed into pure CO(2) and pure C(2)H(2). These decomposed aerosols were characterized through (i) a comparison to experimentally prepared aerosols of mixed CO(2) and C(2)H(2) of known architectures and (ii) the modeling of infrared spectra. A likely architecture after decomposition are C(2)H(2)-CO(2) core-shell particles with a disk-like shape. The co-crystalline CO(2)·C(2)H(2) aerosols prior to decomposition are modeled and analyzed in detail in the subsequent paper (Part II).

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Section: A Pure Co 2 and Pure C 2 H 2 Aerosolsmentioning

confidence: 67%

Infrared spectroscopy and modeling of co-crystalline CO2·C2H2 aerosol particles. I. The formation and decomposition of co-crystalline CO2·C2H2 aerosol particles

Preston

Wang

Signorell

2012

The Journal of Chemical Physics

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“…They are called LO modes, and they always appear at higher frequencies than the TO modes. The theory describing the properties of these surface or longitudinal modes, and the spectral features that can appear between the LO and TO frequencies, have been extensively described in the literature (27,(32)(33)(34)(35)(36). The magnitude of the LO-TO separation is given by…”

Section: Methodsmentioning

confidence: 99%

Crystallization of CO ₂ ice and the absence of amorphous CO ₂ ice in space

Escribano

Muñoz

Cruz-Díaz

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Carbon dioxide (CO 2 ) is one of the most relevant and abundant species in astrophysical and atmospheric media. In particular, CO 2 ice is present in several solar system bodies, as well as in interstellar and circumstellar ice mantles. The amount of CO 2 in ice mantles and the presence of pure CO 2 ice are significant indicators of the temperature history of dust in protostars. It is therefore important to know if CO 2 is mixed with other molecules in the ice matrix or segregated and whether it is present in an amorphous or crystalline form. We apply a multidisciplinary approach involving IR spectroscopy in the laboratory, theoretical modeling of solid structures, and comparison with astronomical observations. We generate an unprecedented highly amorphous CO 2 ice and study its crystallization both by thermal annealing and by slow accumulation of monolayers from the gas phase under an ultrahigh vacuum. Structural changes are followed by IR spectroscopy. We also devise theoretical models to reproduce different CO 2 ice structures. We detect a preferential in-plane orientation of some vibrational modes of crystalline CO 2 . We identify the IR features of amorphous CO 2 ice, and, in particular, we provide a theoretical explanation for a band at 2,328 cm −1 that dominates the spectrum of the amorphous phase and disappears when the crystallization is complete. Our results allow us to rule out the presence of pure and amorphous CO 2 ice in space based on the observations available so far, supporting our current view of the evolution of CO 2 ice.astrochemistry | solid state morphology C arbon dioxide (CO 2 ) has come to play a fundamental role in several aspects of the Earth's geophysics (1, 2), but it is also a key element in astrophysical research (3, 4). In the interior of dense interstellar clouds, as well as in the envelopes around young stars, dust grains are covered by ice mantles formed by frozen volatile molecules, with water being the most abundant molecular species, followed by carbon monoxide (CO), CO 2 , methanol, methane, and others (5, 6). The structure of CO 2 in the icy phase of the interstellar grains is still an open question. Is CO 2 mixed up with other frozen components, or is it segregated in multilayer structures (7)? Has it attained a crystalline arrangement, or does it have an amorphous structure (8)? Because solid CO 2 is an indicator of the temperature history in the envelopes of young stars (9, 10), it is important to address these questions. Most of the available information on these systems comes from spectroscopic observations. Thus, many laboratory experiments have been performed on low-temperature CO 2 , both as a single species and mixed with other components, using IR spectroscopy as the main detection tool (11-15). In the context of solid-state physics, the existence of transverse optical (TO) and longitudinal optical (LO) modes in amorphous materials was questioned because the origin of this effect was linked to long-range order in crystals, but it was proved that longitudinal mode...

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“…Briefly, it is a quantum mechanical model to calculate the IR extinction spectra for molecular nanoparticles. It has been previously shown that for vibrations with a transition dipole moment greater than 0.1 D, the dominant contribution to the IR band shape is resonant dipole coupling (exciton coupling) [1,[34][35][36][37][38][39][40][41][42][43][44][45]. This coupling lifts the degeneracy of the uncoupled molecular vibrational states and leads to vibrational eigenfunctions that are delocalised over the particle.…”

Section: Vibrational Exciton Calculationsmentioning

confidence: 99%

“…A detailed description of this model can be found elsewhere [1,[34][35][36][37]. Briefly, it is a quantum mechanical model to calculate the IR extinction spectra for molecular nanoparticles.…”

Section: Vibrational Exciton Calculationsmentioning

confidence: 99%

Infrared spectroscopy of solid mixed ammonia–water and acetylene–water aerosol particles

Isenor

Signorell

2014

Molecular Physics

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Mixed water aerosols are important components of planetary and lunar atmospheres. In this work, we use rapid-scan Fourier transform infrared (IR) spectroscopy to study solid ammonia-water and acetylene-water aerosol particles formed in a bath gas cooling cell at 78 K. With this set-up, we record time-dependent extinction spectra of particle ensembles in the mid-IR to monitor changes to the internal structure of the aerosol particles. Both ammonia-water and acetylene-water were found to form molecularly mixed structures. The mixing is observed by monitoring the profile for the ammonia ν 2 band and the acetylene ν 5 band, both of which are sensitive to particle properties. Depending on the injection conditions, the mixed particles form either immediately after sample injection or after a short mixing period of several tens of minutes. We confirm the formation of mixed particles by comparing the experimental spectra with spectra calculated with the vibrational exciton model.

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Verification of the vibrational exciton approach for CO2 and N2O nanoparticles

Cited by 52 publications

References 51 publications

Infrared spectroscopy and modeling of co-crystalline CO2·C2H2 aerosol particles. I. The formation and decomposition of co-crystalline CO2·C2H2 aerosol particles

Infrared spectroscopy and modeling of co-crystalline CO2·C2H2 aerosol particles. I. The formation and decomposition of co-crystalline CO2·C2H2 aerosol particles

Crystallization of CO ₂ ice and the absence of amorphous CO ₂ ice in space

Infrared spectroscopy of solid mixed ammonia–water and acetylene–water aerosol particles

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Verification of the vibrational exciton approach for CO2 and N2O nanoparticles

Cited by 52 publications

References 51 publications

Infrared spectroscopy and modeling of co-crystalline CO2·C2H2 aerosol particles. I. The formation and decomposition of co-crystalline CO2·C2H2 aerosol particles

Infrared spectroscopy and modeling of co-crystalline CO2·C2H2 aerosol particles. I. The formation and decomposition of co-crystalline CO2·C2H2 aerosol particles

Crystallization of CO 2 ice and the absence of amorphous CO 2 ice in space

Infrared spectroscopy of solid mixed ammonia–water and acetylene–water aerosol particles

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Crystallization of CO ₂ ice and the absence of amorphous CO ₂ ice in space