Curvilinear kinetic energy models are developed for variational nuclear motion computations including the inter- and the low-frequency intra-molecular degrees of freedom of the formic acid dimer. The coupling of the inter- and intra-molecular modes is studied by solving the vibrational Schrödinger equation for a series of vibrational models, from two up to ten active vibrational degrees of freedom by selecting various combinations of active modes and constrained coordinate values. Vibrational states, nodal assignment, and infrared vibrational intensity information is computed using the the full-dimensional potential energy surface (PES) and electric dipole moment surface developed by Qu and Bowman [Phys. Chem. Chem. Phys. 18, 24835 (2016); J. Chem. Phys. 148, 241713 (2018)]. Good results are obtained for several fundamental and combination bands in comparison with with jet-cooled vibrational spectroscopy experiments, but the description of the $ν_8$ and $ν_9$ fundamental vibrations, which are close in energy and have the same symmetry, appears to be problematic. For further progress in comparison with experiment, the potential energy surface, and in particular, its multi-dimensional couplings representation, requires further improvement.
Formic acid is known to act as a reduction agent for copper oxide. Its thermal uni-molecular decomposition was studied by means of DFT with special attention to reaction paths and kinetics.
Four cluster models for a copper(I)oxide (111) surface have been designed, of which three were studied with respect to their applicability in density functional calculations in the general gradient approximation. Formic acid adsorption on these systems was modelled and yielded four different adsorption structures, of which two were found to have a high adsorption energy. The energetically most favourable adsorption structure was further investigated with respect to its decomposition and a few reactions with adsorbed H and OH species using synchronous transit methods to estimate reaction barrie…
In this paper, we discuss the dissociative electron attachment process in Formic Acid and Propyl Amine. These are molecules containing more than one functional group and have low symmetry (Cs group). We measured the kinetic energy and angular distributions of fragment H^{-} ions from the resonances observed in these molecules and compared with that in the precursor molecules, namely - Water, Ammonia and Methane. Measurements suggest that the dissociation dynamics in bigger molecules are independent of overall symmetry of the molecule, rather depend only on the local symmetry of functional grou…
The ground-state energy and density of four low-energy conformations of the formic acid dimer were calculated via Partition Density Functional Theory (PDFT). The differences between isolated and PDFT monomer densities display similar deformation patterns for primary and secondary hydrogen bonds among all four dimers. In contrast, the partition potential shows no transferable features in the bonding regions. These observations highlight the global character of the partition potential and the cooperative effect that occurs when a dimer is bound via more than one hydrogen bond. We also provide nu…
The ring-polymer instanton approach is applied to compute the ground-state tunnelling splitting of four isotopomers of the formic acid dimer using the accurate PES of Qu and Bowman [Phys. Chem. Chem. Phys., 2016, 18, 24835]. As well as performing the calculations in full dimensionality, we apply a reduced-dimensionality approach to study how the results converge as successively more degrees of freedom are included. The instanton approximation compares well to exact quantum results where they are available but shows that nearly all the modes are required to quantitatively obtain the tunnelling …
The intramolecular vibrational relaxation dynamics of formic acid and its deuterated isotopologues is simulated on the full-dimensional potential energy surface of Richter and Carbonniere [F. Richter and P. Carbonniere, J. Chem. Phys., 148, 064303 (2018)] using the Heidelberg MCTDH package. Mode couplings with the torsion coordinate capturing most of the trans-cis isomerisation are identified in the dynamics of artificially excited vibrational mode overtones. The C-O stretch bright vibrational mode is coupled to the out-of-the plane torsion mode in HCOOH, where this coupling could be exploited…
We report the results of a joint experimental {and} theoretical study of dissociative electron attachment to formic acid (HCOOH) in the 6-9 eV region, where H$^-$ fragment ions are a dominant product. Breaking of the CH and OH bonds is distinguished experimentally by deuteration of either site. We show that in this region H$^-$ ions can be produced by formation of two {or possibly three} Feshbach resonance (doubly-excited anion) states, one of which leads to either C-H or O-H bond scission, while the other can only produce formyloxyl radicals by O-H bond scission. Comparison of experimental an…
An electro-optic dual comb system based on chirped-pulse waveforms is used to simultaneously acquire temporally magnified rapid passage signals and normal spectral line shapes from the back-transformation to the time domain. Multi-heterodyne THz wave generation and detection is performed with the difference frequency mixing of two free-running lasers. The method is used to obtain THz spectra of formic acid in the 10 cm-1 to 20 cm-1 (300 GHz to 600 GHz) region over a range of pressures. The method is widely applicable across other spectral regions for investigations of the transient dynamics an…
The double proton transfer (DPT) reaction in hydrated formic acid dimer (FAD) is investigated at molecular-level detail. For this, a global and reactive machine learned (ML) potential energy surface (PES) is developed to run extensive (more than 100 ns) mixed ML/MM molecular dynamics (MD) simulations in explicit molecular mechanics (MM) solvent at MP2-quality for the solute. Simulations with fixed - as in a conventional empirical force field - and conformationally fluctuating - as available from the ML-based PES - charge models for FAD shows significant impact on the competition between DPT an…
In recent years, machine learning potentials (MLP) for atomistic simulations have attracted a lot of attention in chemistry and materials science. Many new approaches have been developed with the primary aim to transfer the accuracy of electronic structure calculations to large condensed systems containing thousands of atoms. In spite of these advances, the reliability of modern MLPs in reproducing the subtle details of the multi-dimensional potential-energy surface is still difficult to assess for such systems. On the other hand, moderately sized systems enabling the application of tools for …
The vibrational dynamics of formic acid monomer (FAM) and dimer (FAD) is investigated from machine-learned potential energy surfaces at the MP2 (PES$_{\rm MP2}$) and transfer-learned (PES$_{\rm TL}$) to the CCSD(T) levels of theory. The normal modes and anharmonic frequencies of all modes below 2000 cm$^{-1}$ agree favourably with experiment whereas the OH-stretch mode is challenging for FAM and FAD from normal mode analyses and finite-temperature MD simulations. VPT2 calculations on PES$_{\rm TL}$ for FAM reproduce the experimental OH frequency to within 22 cm$^{-1}$. For FAD the VPT2 calcula…
The effect of ethanol-water media on the synthesis of Ag/TiO2 nanocomposite was investigated with 0.05, 0.1 and 0.5 (wt.%) of Ag content. Ethanol was used as hole-scavenger enhancing the photodecomposition of Ag+ ions under illumination of near-UV light. The nanocomposites were further calcined to 33C and 400C under controlled atmosphere. The synthesized nanocomposites were tested for photocatalytic efficiency decomposing formic acid as an organic pollutant under irradiation of a 4W near UV lamp with lmax at 365nm and the results were compared with that of nan-modified commercially available D…
In order to better understand their potential formation in combustion systems, a detailed kinetic mechanism for the formation of short-chain monocarboxylic acids, formic (HCOOH), acetic (CH3COOH), propionic (C2H5COOH) and propenic (C2H3COOH)) acids, has been developed. Simulations of lean (equivalence ratios from 0.9 to 0.48) laminar premixed flames of propane stabilized at atmospheric pressure with nitrogen as diluent have been performed. It was found that amounts up to 25 ppm of acetic acid, 15 ppm of formic acid and 1 ppm of C3 acid can be formed for some positions in the flames. Simulation…
We studied theoretically the cis-trans isomerization reactions of two astrophysically relevant acids, formic acid (HCOOH) and thioformic acid (HC(O)SH), where the latter has recently been discovered in space. We also searched for these molecules towards the hot core G31.41+0.31 to compare their abundances with the expected theoretical isomerization results. Our results demonstrate that these isomerizations are viable in the conditions of the ISM due to ground-state tunneling effects, which allow the system to reach the thermodynamic equilibrium at moderately low temperatures. At very low tempe…
Vibrational states of the formic acid molecule are converged using the GENIUSH-Smolyak approach and the potential energy surface taken from [D. Tew and W. Mizukami, J. Phys. Chem. A 120, 9815 (2016)]. The quantum nuclear motion is described by using the $cis$-$trans$ torsional coordinate and eight curvilinear normal coordinates defined with respect to an instantaneous reference configuration changing as a function of the torsional degree of freedom. Harmonic oscillator basis functions are used for the curvilinear normal coordinates, a Fourier basis for the torsional coordinate, and a simple ba…
Thioformic acid (TFA) is the sulfur analog of formic acid, the simplest organic acid. It has three analogues HCOSH, HCSOH, and HCSSH, each of them having two rotational isomeric (rotameric) forms: trans and cis where the trans form is energetically more stable. In this article, we study computational energetics and anharmonic vibrational spectrum of TFA including overtone and combination vibrations. We also studied experimental photoisomerization and photodecomposition channels of HCOSH molecules with different wavelengths. We suggest that TFA is a potential sulfur containing candidate molecul…
Rotation-vibration spectra of the nitric acid molecule, HNO\3, are calculated for wavenumbers up to 7000~\cm. Calculations are performed using a Hamiltonian expressed in internal curvilinear vibrational coordinates solved using a hybrid variational-perturbation method. An initial potential energy surface (PES) and dipole moment function (DMF) are calculated {\it ab initio} at the CCSD(T)/aug-cc-pVQZ level of theory. Parameters of the PES and DMF are varied to minimize differences between the calculated and experimental transition frequencies and intensities. The average, absolute deviation bet…
Acetaldehyde (AA) isomerization (to vinylalcohol, VA) and decomposition (into either CO+CH$_4$ and H$_2$+H$_2$CCO) is studied using a fully dimensional, reactive potential energy surface represented as a neural network (NN). The NN, trained on 432'399 reference structures from MP2/aug-cc-pVTZ calculations has a MAE of 0.0453 kcal/mol and an RMSE of 1.186 kcal/mol for a test set of 27'399 structures. For the isomerization process AA $\rightarrow$ VA the minimum dynamical path implies that the C-H vibration, and the C-C-H (with H being the transferring H-atom) and the C-C-O angles are involved t…
