1,720,974 research outputs found
CC-stretched formic acid: isomerisation, dimerisation, and carboxylic acid complexation
No full textThe cis – trans -isomerism of the propiolic acid monomer (HCC–COOH) is examined with linear Raman jet spectroscopy, yielding the first environment-free vibrational band centres of a higher-energy cis -rotamer beyond formic acid (HCOOH) in addition to all fundamentals and a large number of hot and combination/overtone bands of the trans -conformer.The cis – trans -isomerism of the propiolic acid monomer (HCC–COOH) is examined with linear Raman jet spectroscopy, yielding the first environment-free vibrational band centres of a higher-energy cis -rotamer beyond formic acid (HCOOH) in addition to all fundamentals and a large number of hot and combination/overtone bands of the trans -conformer. Two near-isoenergetic trans -fundamentals of different symmetry (CCO bend and OH torsion) prove to be a sensitive benchmarking target, as their energetic order is susceptible to the choice of electronic structure method, basis set size, and inclusion of vibrational anharmonicity. For the infrared- and Raman-active CO stretching fundamentals of the cyclic ( C 2h ) trans -propiolic acid dimer, resonance couplings are found that in part extend to the C s -symmetric heterodimer of trans -propiolic and trans -formic acid. Exploratory vibrational perturbation theory (VPT2) calculations show that all perturbing states involve displacements of the OH moieties located on the doubly hydrogen bonded ring. The comparison of the infrared spectra of the propiolic acid dimer and its heterodimer with formic acid to that of several other carboxylic acid dimers from the literature reveals a notable similarity regarding a non-fundamental dimer band around 1800 cm −1 , which in most cases is so far unassigned. VPT2 calculations and a simple harmonic model suggest an assignment to a combination vibration of the symmetric and antisymmetric OH torsion.The cis – trans -isomerism of the propiolic acid monomer (HCC–COOH) is examined with linear Raman jet spectroscopy, yielding the first environment-free vibrational band centres of a higher-energy cis -rotamer beyond formic acid (HCOOH) in addition to all fundamentals and a large number of hot and combination/overtone bands of the trans -conformer.The cis – trans -isomerism of the propiolic acid monomer (HCC–COOH) is examined with linear Raman jet spectroscopy, yielding the first environment-free vibrational band centres of a higher-energy cis -rotamer beyond formic acid (HCOOH) in addition to all fundamentals and a large number of hot and combination/overtone bands of the trans -conformer. Two near-isoenergetic trans -fundamentals of different symmetry (CCO bend and OH torsion) prove to be a sensitive benchmarking target, as their energetic order is susceptible to the choice of electronic structure method, basis set size, and inclusion of vibrational anharmonicity. For the infrared- and Raman-active CO stretching fundamentals of the cyclic ( C 2h ) trans -propiolic acid dimer, resonance couplings are found that in part extend to the C s -symmetric heterodimer of trans -propiolic and trans -formic acid. Exploratory vibrational perturbation theory (VPT2) calculations show that all perturbing states involve displacements of the OH moieties located on the doubly hydrogen bonded ring. The comparison of the infrared spectra of the propiolic acid dimer and its heterodimer with formic acid to that of several other carboxylic acid dimers from the literature reveals a notable similarity regarding a non-fundamental dimer band around 1800 cm −1 , which in most cases is so far unassigned. VPT2 calculations and a simple harmonic model suggest an assignment to a combination vibration of the symmetric and antisymmetric OH torsion
-formic acid and its deuterated isotopologs: Combining theory and experiment to extend the vibrational database
No full textIncreasing the weights in the molecular work-out of cis - and trans -formic acid: extension of the vibrational database via deuteration
No full textCoupled proton vibrations between two weak acids: the hinge complex between formic acid and trifluoroethanol
No full textRaman and FTIR spectra of an acid–alcohol complex show complementary signatures from acidic and alcoholic OH stretching, proving its existence.When formic acid and 2,2,2-trifluoroethanol are co-expanded through a slit nozzle into vacuum, a single dominant, hinge-like 1 : 1 complex is formed in significant amounts and its two OH stretching fundamentals separated by 100 cm
−1
can be unambiguously assigned by a combination of infrared absorption and Raman scattering. Quantum chemical calculations at different levels reproduce this finding in a satisfactory way and suggest that in-phase (Raman-sensitive and lower wavenumber) OH stretch excitation more or less along the concerted degenerate proton transfer coordinate in the hydrogen-bonded ring stays below the barrier for this concerted exchange. Anharmonic calculations indicate only weak intensity sharing with dark states coming into reach due to the hydrogen bond downshift of the OH stretching vibration. This well-behaved system sets the stage for acid combinations with more basic alcohols, where the in-phase OH stretching vibration is more difficult to detect, possibly due to fast intra-complex vibrational dynamics. It thus provides a benchmark point from which one can explore the evolution of vibrational resonances when the acidic proton meets a more electron-rich alcoholic oxygen.Deutsche Forschungsgemeinschaft https://doi.org/10.13039/50110000165
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