How Much Water Is Needed To Ionize Formic Acid?

Abstract

Structure, molecular properties, energy parameters, and vibrational IR spectra of hydrated clusters of formic acid (FOH), FOH·nH2O (n = 1-8), are presented following first principle based electronic structure theory. Several geometrical arrangements are considered as initial guess structures to look for the minimum energy equilibrium structures applying ωB97X-D density functional and aug-cc-pVDZ set of atomic basis functions. Results on FOH-water clusters suggest that the most stable structure of formic acid exists as a charge-separated ion pair, FO(-δ)---H(+δ)---O(-δ)H2, in hydrated clusters, FOH·nH2O, for cluster size n ≥ 7. The calculated interaction energy between FOH and the solvent water cluster increases significantly by adding the seventh solvent water molecule to the FOH·6H2O cluster whereas the solvent stabilization energy of FOH increases continuously on successive addition of solvent water molecules (n = 1-8). Energy partitioning of the solvent stabilization energy of FOH·nH2O clusters suggests an electrostatic component of energy to play the major role in solvent stability and does depict sudden variation for n = 7. Formation of a charge-separated ion pair for cluster size n ≥ 7 is manifested in simulated IR spectra of FOH·nH2O clusters. Static polarizabilities of hydrated formic acid clusters are calculated and observed to vary linearly with the size of the clusters, suggesting reliability in prediction of polarizability for larger size hydrated clusters of formic acid.

Microhydration and the Enhanced Acidity of Free Radicals

“…n H 2 O.H + ) took place for some value of n (= N G i ). Microhydrated cluster structures published by Maity and co-workers for structurally analogous formic [ 27 ] and trifluoroacetic acid [ 28 ] and by Leopold for various acids [ 21 ] served as useful models for the starting points for optimizations. The larger hydration clusters ( n > ~8) displayed potential energy surfaces with quite a lot of shallow local minima, such that extensive searching was needed to find the global minima.…”

Ultrafast Proton Transfer Reaction in Phenol–(Ammonia)n Clusters: An Ab-Initio Molecular Dynamics Investigation.

“…More importantly, the general interest is to probe the minimum number of solvent molecules required for acid dissociation and concurrent proton transfer process, to understand the acid dissociation phenomenon at a molecular level. [2][3][4][5][6] In this regard, the role of ammonia as a solvent in the proton transfer process in the phenol-(ammonia)n clusters have been the subject of intense experimental and theoretical investigations by several research groups over the past three decades to understand the proton transfer reaction in the ground state and hydrogen transfer process in the excited electronic state. [7][8][9][10][11][12][13][14][15][16] Additionally, it has been shown that the excited proton transfer reaction of phenol becomes ultrafast at the air-water interface.…”

Isolating the spectral signature of H3O+ in the smallest droplet of dissociated HCl acid

“…In this report, we present a calculation of the IR spectrum of the SIP in a fashion that isolates the contribution from the signature hydronium ion, H 3 Fundamental studies of acids in biological and chemical contexts are obviously of great and intense interest. [6][7][8][9][10][11][12] The answer is typically sought by detecting the presence or absence of signature spectral features of the hydrated proton in the infra-red. [6][7][8][9][10][11][12] The answer is typically sought by detecting the presence or absence of signature spectral features of the hydrated proton in the infra-red.…”