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Formic and acetic acids in a nitrogen matrix: Enhanced stability
Lopes, Susy; Domanskaya, Alexandra V; Fausto, Rui; Räsänen, Markku; Khriachtchev, LeonidFormic acid HCOOH, FA and acetic acid CH3COOH, AA are studied in a nitrogen matrix. The infrared IR spectra of cis and trans conformers of these carboxylic acids and also of the HCOOD isotopologue of FA are reported and analyzed. The higher-energy cis conformer of these molecules is produced by narrowband near-IR excitation of the more stable trans conformer, and the cis-to-trans tunneling decay is eval...
Rotational isomerization of small carboxylic acids isolated in argon matrices: ...
Maçôas, Ermelinda M. S.; Khriachtchev, Leonid; Pettersson, Mika; Fausto, Rui; Räsänen, MarkkuThe quantum yields for internal rotation around the C–O bond induced by excitation of the first overtone of the hydroxyl stretching mode in formic, acetic, and propionic acids isolated in solid Ar are comparatively discussed. The tunnelling kinetics for isomerization from the higher energy arrangement of the carboxylic group (cis) to the lower energy arrangement (trans) in this series of compounds is also analy...
Internal Rotation in Propionic Acid: Near-Infrared-Induced Isomerization in So...
Maçôas, Ermelinda M. S.; Khriachtchev, Leonid; Pettersson, Mika; Fausto, Rui; Räsänen, MarkkuThe conformational system of propionic acid (CH3CH2COOH) is studied in solid argon. It is predicted by the ab initio calculations that this molecule has four stable conformers. These four structures are denoted Tt, Tg±, Ct, and Cg±, and they differ by the arrangement around the C−O and Cα−C bonds. The ground-state Tt conformer is the only form present at 8 K after deposition of an argon matrix containing propio...
Infrared-induced conformational interconversion in carboxylic acids isolated in...
Maçôas, Ermelinda M. S.; Khriachtchev, Leonid; Pettersson, Mika; Lundell, Jan; Fausto, Rui; Räsänen, MarkkuAn overview of our recent studies dealing with infrared-induced conformational interconversion of carboxylic acids isolated in rare-gas matrices is presented. Extensive rotational photoisomerization studies have been performed on formic acid, which is the simplest organic acid enabling this kind of processes. Formic acid has two conformers and interconversion between them can be induced by vibrational excitatio...
Vibrational spectroscopy of cis- and trans-formic acid in solid argon
Maçôas, Ermelinda M. S.; Lundell, Jan; Pettersson, Mika; Khriachtchev, Leonid; Fausto, Rui; Räsänen, MarkkuAbsorption spectra of cis and trans conformers of formic acid (HCOOH) isolated in solid argon are analyzed in the mid-infrared (4000-400 cm-1) and near-infrared (7800-4000 cm-1) regions. The HCOOH absorption spectrum reveals matrix-site splitting for the trapped molecule. Narrowband tunable infrared radiation is used to pump a suitable vibrational transition of the trans conformer in order to promote site-selec...
Rotational Isomerism in Acetic Acid: The First Experimental Observation of the...
Maçôas, Ermelinda M. S.; Khriachtchev, Leonid; Pettersson, Mika; Fausto, Rui; Räsänen, MarkkuThe high-energy conformer of acetic acid (cis-AA) is produced in an Ar matrix by vibrational excitation of the OH stretching overtone of the ground conformational state (trans-AA). IR-absorption spectroscopy provides a clear identification of the reaction product. cis-AA converts back to trans-AA in a time scale of minutes at 8 K by tunneling. ; http://dx.doi.org/10.1021/ja038341a
Conformational Isomerization of Formic Acid by Vibrational Excitation at Energi...
Pettersson, Mika; Maçôas, Ermelinda M. S.; Khriachtchev, Leonid; Fausto, Rui; Räsänen, MarkkuPhotoinduced conformational isomerization of formic acid has been studied in a low-temperature argon matrix. It is found that conformational isomerization occurs when the photon energy is below the energy barrier for this process. The quantum yield for the process near the top of the barrier is comparable with the quantum yield above the barrier and drops at lower energies. The isomerization takes place via a t...
A Matrix Isolation Spectroscopic and Quantum Chemical Study of Fumaric and Male...
Maçôas, Ermelinda M. S.; Fausto, Rui; Lundell, Jan; Pettersson, Mika; Khriachtchev, Leonid; Räsänen, MarkkuRelative energies and vibrational spectra of buthenedioic acid [(E)- and (Z)-HOOC−CHCH−COOH; fumaric and maleic acids] were calculated using Hartree−Fock (HF), Møller−Plesset to 2nd order (MP2), and B3LYP Density Functional Theory (DFT) levels of approximation. Computationally the lowest energy conformer of maleic acid has a nearly planar structure with an OH···OC intramolecular hydrogen bond closing a seven me...
Infrared-Induced Rotamerization of Oxalic Acid Monomer in Argon Matrix
Maçôas, Ermelinda M. S.; Fausto, Rui; Pettersson, Mika; Khriachtchev, Leonid; Räsänen, MarkkuInfrared-induced conformational isomerization of oxalic acid monomer isolated in an argon matrix at 7.5 K was studied by infrared spectroscopy. For the first time, three conformational states of this molecule were identified experimentally and their vibrational spectra are assigned. In good agreement with density functional theory predictions, all the observed conformers exhibit a trans OC−CO axis, differing in...
Conformational Analysis and Near-Infrared-Induced Rotamerization of Malonic Aci...
Maçôas, Ermelinda M. S.; Fausto, Rui; Lundell, Jan; Pettersson, Mika; Khriachtchev, Leonid; Räsänen, MarkkuRelative energies and vibrational spectra of the conformational states of a malonic acid monomer (HOOCCH2COOH) were calculated using various levels of approximation [Hartree−Fock (HF), Møller−Plesset to second order (MP2), and B3LYP density functional theory (DFT)]. The calculations predict the existence of six different conformers according to skeletal C−C bond and O−H bond rotation. Three conformers are found...
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