Cesium atoms in cryogenic argon matrix

This paper presents both experimental and theoretical investigations into the spectroscopy of dilute cesium (Cs) atoms within a solid argon (Ar) matrix at cryogenic temperatures. This system is relevant for matrix isolation spectroscopy and in particular for recently proposed methods for investigating phenomena that extend beyond the standard model of particle physics. We record absorption spectra at various deposition temperatures and examine the evolution of these spectra post-deposition with respect to temperature changes. Taking advantage of Cs-Ar and Ar-Ar pairwise interaction potentials, we conduct a stability study of trapping sites, which indicates a preference for T$_{\rm d}$ (tetrahedral, 4 vacancies) and O$_{\rm h}$ (cubic, 6 vacancies) symmetries. By implementing a mean-field analysis of the long-range Cs(6s,6p)-Ar-Ar triple dipole interaction, combined with a temperature-dependent shift in zero point energy, we propose effective Cs(6s,6p)-Ar pairwise potentials. Upon integrating these pairwise potentials with spin-orbit coupling, we achieve a satisfactory agreement between the observed and simulated absorption line positions. The observed line broadening is reasonably well reproduced by a semi-classical thermal Monte Carlo approach based on Mulliken-type differences between excited and ground potential curves. Additionally, we develop a simple, first-order crystal field theory featuring only 6 interaction mode coordinates. It uses the reflection approximation and incorporates quantized (phonon) normal modes. This produces a narrow triplet structure but not the observed amount of splitting

Electronic relaxation of aniline in argon matrix: A site selective laser spectroscopy

International audienceAbsorption (S1←S0), fluorescence (S1→S0) and phosphorescence (T1→S0) spectra of aniline isolated in argon matrices are presented and analyzed. Upon selective laser excitation, two families of sites are characterized by electronic spectroscopy and excited state dynamics. A strong electron/phonon coupling is observed in the S1↔S0 transition due to a geometry change of the molecule. Phosphorescence spectra exhibit different vibronic intensity distribution for both sites; a1 in plane and b1 out-of-plane modes are observed. A direct estimation of the inversion splitting in the ground state (46 cm−1) is obtained from the presence of an intense doublet assigned to 3A1(0+)→1A1(0+,0−) vibronic transitions

Infrared spectroscopy of aniline (C6H5NH2) and its cation in a cryogenic argon matrix

International audienceInfrared absorption spectra of aniline, trapped in a low-temperature 5 K argon matrix, have been obtained in the spectral region from 500 to 4000 cm−1. The aniline cation C6H7N+, was formed inside the matrix by UV laser irradiation. We report the first IR absorption spectroscopy of this cation in an argon matrix: five fundamental vibrational bands were observed

Phosphorescence of C 5 N − in Rare Gas Solids

International audiencePhosphorescence of C5N− was discovered following the ArF-laser (193 nm) photolysis of cyanodiacetylene (HC5N) isolated in cryogenic argon, krypton, and xenon matrices. This visible emission, with an origin around 460 nm, is vibrationally resolved, permitting the measurement of frequencies for eight ground-state fundamental vibrational modes, including the three known from previous IR absorption studies. Phosphorescence lifetime amounts to tens or even hundreds of ms depending on the matrix host; it is five times longer than in the case of HC5N

Selective photoisomerisation of 2-chloromalonaldehyde

International audienceIsomerization of 2-chloromalonaldehyde (2-ClMA) is explored giving access to new experimental data on this derivative of mal-onaldehyde, not yet studied much. Experiments were performed isolating 2-ClMA in argon, neon, and para-hydrogen matrices. UV irradiation of the matrix samples induced isomerization to three open enolic forms including two previously observed along with the closed enolic form after deposition. IR spectra of these specific conformers were recorded, and a clear assignment of the observed bands was obtained with the assistance of theoretical calculations. UV spectra of the samples were measured , showing a blue shift of the π * ← π absorption with the opening of the internal hydrogen bond of the most stable enol form. Specific sequences of UV irradiation at different wavelengths allowed us to obtain samples containing only one enol conformer. The formation of conformers is discussed. The observed selectivity of the process among the enol forms is analyzed. Published under license by AIP Publishing. https://doi

Intramolecular hydrogen tunneling in 2-chloromalonaldehyde trapped in solid para -hydrogen

International audienceInternal dynamics of 2-chloromalonaldehyde (2-ClMA) molecule, possessing strong internal hydrogen bond (IHB) was examined by means of matrix isolation spectroscopy in a soft host: para-hydrogen (pH2). 2-ClMA is a chlorinated derivative of malonaldehyde (MA), a model molecule in hydrogen transfer studies, better suited to low temperature experiments than its parent molecule. The infrared absorption spectra of 2-ClMA isolated in pH2 exhibit temperature dependent structures which are explained as transitions occurring from split vibrational levels induced by hydrogen tunneling. The doublet components associated with higher and lower energy levels are changing reversibly with the increase/decrease of the matrix temperature. The ground state splitting is measured to 7.90.1 cm-1. The presence of oH2 impurities in pH2 matrix close to the neighborhood of the 2-ClMA molecule is found to quench the H tunneling. The data provide a powerful insight into the dynamical picture of intramolecular hydrogen tunneling in a molecule embedded in a very weakly perturbing environment

Low Temperature Synthesis and Phosphorescence of Methylcyanotriacetylene

International audienceThis paper reports on UV-stimulated synthesis of methylcyanotriacetylene carried out in cryogenic rare gas matrixes via coupling of smaller precursors: propyne and cyanodiacetylene. The detection was possible due to the strong visible ã 3A' → X̃ 1A1 phosphorescence of CH3C7N, discovered in the course of this work. The ensuing measurements of electronic spectroscopy revealed the formally forbidden B̃ 1E-X̃ 1A1 system, as well as the allowed one Ẽ 1A1-X̃ 1A1, with origins at approximately 3.32 and 5.4 eV, respectively. It was also possible to revisit the spectroscopic characterization of cyanotriacetylene, HC7N, formed in parallel to the title photoproduct. Spectral assignments were assisted with a density functional theory study

Hidden Isomer of Trifluoroacetylacetone Revealed by Matrix Isolation Infrared and Raman Spectroscopy

International audienceEnol forms of trifluoroacetylacetone (TFacac) isolated in molecular and rare gas matrices were studied using infrared (IR) and Raman spectroscopy. Additionally, calculations using DFT B3LYP and M06-2X as well as MP2 methods were performed in order to investigate the possibility of coexistence of more than one stable enol form isomer of TFacac. Calculations predict that both stable enol isomers of TFacac, 1,1,1-trifluoro-4-hydroxy-3-penten-2-one (1) and 5,5,5-trifluoro-4-hydroxy-3-penten-2-one (2), could coexist, especially in matrices where the room temperature population is frozen, 1 being the most stable one. Raman and IR spectra of TFacac isolated in nitrogen (N2) and carbon monoxide (CO) matrices exhibit clear absorption bands, which cannot be attributed to this single isomer. Their relative band positions and intensity profiles match well with the theoretical calculations of 2.This allows us to confirm that in N2 and CO matrices both isomers exist in similar amounts. Careful examination of the spectra of TFacac in argon, xenon, neon, normal, and para-hydrogen (Ar, Xe, Ne, nH2, and pH2 respectively) matrices revealed that both isomers coexist in all the explored matrices, whereas 2 was not considered in the previous spectroscopic works. The amount of the second isomer (2) in the as-deposited samples depends on the host. The analysis of TFacac spectra in the different hosts and under various experimental conditions allows the vibrational characterization of both chelated isomers. The comparison with theoretical predictions is also investigated

Revisiting photoisomerization in fluorinated analogues of acetylacetone trapped in cryogenic matrices

UV-induced processes are commonly studied in acetylacetone analogues. In this contribution, we revisit the existing work on the photoisomerization process in some of the fluorinated analogues of acetylacetone, i.e., trifluoroacetylacetone (F3-acac) and hexafluoroacetylacetone (F6-acac). We performed selective UV laser excitation of these molecules trapped in soft cryogenic matrices, namely neon and para-hydrogen, and probed by vibrational spectroscopy. Clear spectroscopy of 3 isomers of F6-acac and 6 isomers of F3-acac is obtained, including the first characterization of a second open enol isomer of hexafluoroacetylacetone. In addition, we present the electronic absorption spectra of both molecules in cryogenic matrices before and after specific UV irradiations, giving new data on the electronic transitions of photoproducts. Vibrational and electronic experimental results are analyzed and discussed within comparisons with DFT and TD-DFT calculations. Our findings contribute to a deeper understanding of the photoisomerization process in these molecules after electronic excitation in gas and condensed phase