FIG 2
The potential describing double proton transfer in the benzoic acid dimer. Localized excitation breaks the symmetry of the potential ͑ a ͒ , but coupling between the two asymmetric potentials leads to two symmetric potentials ͑ b ͒ . The coupling shown in ͑ c ͒ can be induced by excitation exchange ͑ horizontal arrows ͒ or by 3 Љ inversion ͑ diagonal arrows ͒ .
Source publication
High resolution ultraviolet spectroscopy has been used to investigate the rotationally resolved excitation spectrum of the first singlet-singlet transition in the benzoic acid dimer. The measured spectrum consists of two overlapping components. The corresponding lines in the two components are shown to originate in different levels of the ground st...
Contexts in source publication
Context 1
... in benzene. Isotope studies show that the excitation is essen- tially localized in one of the monomer units. 5, 28 The two constituents are no longer equivalent after electronic excita- tion, thus the symmetry of the dimer is broken in S 1 . The potential for proton transfer will be given by an asymmetric potential, schematically given in Fig. 2a. However, since no distinction can be made as to which of the two molecules in the dimer is excited, the symmetry in the potential surface must be restored. In general, the two potentials are coupled, which gives rise to a symmetric potential depicted in Fig. 2b. This is similar to the description of the interconversion tunneling in HF ...
Context 2
... for proton transfer will be given by an asymmetric potential, schematically given in Fig. 2a. However, since no distinction can be made as to which of the two molecules in the dimer is excited, the symmetry in the potential surface must be restored. In general, the two potentials are coupled, which gives rise to a symmetric potential depicted in Fig. 2b. This is similar to the description of the interconversion tunneling in HF 2 and HCCH 2 Ref. 32 and of the tun- neling dynamics in the ammonia dimer Ref. ...
Context 3
... coupling in the benzoic acid dimer can be induced by exchange of the excitation from one unit to the other see Fig. 2c. Also inversion along the in-plane intermolecular 3 coordinate can induce coupling between the two poten- tials. The localized excitation increases the basicity of the excited unit and decreases its acidity so that it will act as a proton acceptor, while the nonexcited unit will act as a pro- ton donor. This causes the dimer to bend ...
Citations
... Chemically, in benzoic acid the carboxyl group (-COOH) is attached to a benzene ring. In aqueous the dimerization of crystalline benzoic acid and its carboxylic group is may polarize by formation of H-bonding with water molecule [17,18]. In this work, thermodynamically, at Kelvin temperature range in between 288 K to 318 K, the dissociation constant (Ka) of benzoic acid into aqueous solutions have been determined well by applying of titration method against standard basic solution of NaOH with different value of ionic strength of NaCl. ...
In article, we have reported a thermodynamic based study of aqueous solvation of benzoic acid (C6H5COOH) at 288 to 318 Kelvin temperature. At this temperature range the dissociation constant (Ka) of benzoic acid into aqueous solvent has been determined by applying of titration method against standard basic solution of NaOH at different ionic strength of NaCl. Although, in observation, the value of Ka is being inversely proportional in respect of temperature in between 289 K to 303 K, and at higher temperature in between 303 K to 314 K, it being directly proportional. This reports that, there are no regular correlation in between temperature and Ka of that acid. Graphically, the plot has shown the value of Ka of benzoic acid is being 4.176 at 298 K temperature. In finding of precious results for benzoic acid solvation and its dissociation into water the applying Vant Hoff equation with Gibbs free energy change relationship (∆G = ∆H - T∆S) for reaction (endothermic or exothermic) process at standard condition of thermodynamic parameters as in terms of enthalpy (H) and entropy (S). Where, the thermodynamic parameters value (in kJ.mol-1) are being as ∆G = 12.507, ∆H = 3.823 and ∆S = -29.14, but, at 298 K it is show that, the acid dissociation into aqueous is an endothermic process and non-spontaneous.
... The addition of small amount solute or salts into water has shown an interaction in between solute and solvent. In aqueous the dimerization of crystalline benzoic acid and its carboxylic group is may polarize by formation of H-bonding with water molecule [18,19]. In this work, thermodynamically, at Kelvin temperature range in between 288 K to 318 K, the dissociation constant (Ka) of benzoic acid into aqueous solutions have been determined well by applying of titration method against standard basic solution of NaOH with different value of ionic strength of NaCl. ...
In article, we have reported a thermodynamic based study of the Gibbs free energy change (∆G) in aqueous dissociation of benzoic acid at Kelvin temperature range in between of 288 K to 318 K. Thermodynamically, at this Kelvin temperatures range the dissociation constant (Ka) of benzoic acid into aqueous solutions have been determined by applying of titration method against standard basic solution of NaOH at different concentrations or ionic strength of NaCl. In observation, the value of Ka is being inversely proportional with respect to temperature in between 289 K to 303 K, and at higher temperature in between 303 K to 314 K, it being directly proportional. This is reported that, there are no regular correlation in between temperature and Ka of that acid. In graph, the plot has shown the value of Ka of benzoic acid is being 4.176 at 298 K temperature. Thus, in finding of precious results for benzoic acid dissociation into water an applying the Gibbs free energy change relationship (∆G = ∆H - T∆S) for endothermic or exothermic reaction process at standard condition of thermodynamic parameters. These parameters value (in kJ.mol-1) are being as ∆G = 12.507, ∆H = 3.823 and ∆S = -29.14. And, at 298 K, it is show that the acid dissociation into aqueous solvent is an endothermic and non-spontaneous process with ordered entropy (∆S).
... For (2-pyridone) 2 , (benzonitrile) 2 and (benzoic acid) 2 , the ground-and excited-state gas-phase structures have been determined by laser high-resolution spectroscopy. [35][36][37][38] The infrared and UV spectra of the o-cyanophenol dimer, the m-cyanophenol dimer and the mixed o-cyanophenol-m-cyanophenol dimer have been investigated at vibronic resolution by Lahmani, Zehnacker and co-workers, 39,40 and similarly for the anthranilic acid (2-amino-benzoic acid) dimer by Levy, Zwier and co-workers. 41 We also note several theoretical and spectroscopic studies of the stacked anisole dimer, [42][43][44] although stacked dimers are outside the scope of this short review. ...
... However, no such second electronic origin was identied in any of the discussed complexes. [36][37][38][39][40][41]55 In contrast, our recent work has revealed the appearance of the second 0 0 0 band of (benzoic acid) 2 , (benzonitrile) 2 and (ocyanophenol) 2 if the C 2h symmetry is lowered to C S by isotopic substitution, with concomitant localization of the electronic excitations. 29,30,33 As discussed in Section 5.2, the appearance of non-totally symmetric vibronic excitations is fully compatible with delocalized excitonic states, since the vibronic coupling in weakcoupling systems results in the appearance of additional bands, as shown in Section 5. ...
... Thus the most probable geometry of (benzoic acid) 2 and (benzonitrile) 2 in their S 1 and S 2 excited states should be slightly asymmetric, in agreement with the structures determined by high-resolution laser measurements of the 0 0 0 bands. [36][37][38]54 In a semiclassical picture, the excitation can be considered to be hopping between the A and B chromophores, with a resonance transfer rate 12 ...
After decades of research on molecular excitons, only few molecular dimers are available on which exciton and vibronic coupling theories can be rigorously tested. In centrosymmetric H-bonded dimers consisting of identical (hetero)aromatic chromophores, the monomer electronic transition dipole moment vectors subtract or add, yielding S0 → S1 and S0 → S2 transitions that are symmetry-forbidden or -allowed, respectively. Symmetry breaking by 12C/13C or H/D isotopic substitution renders the forbidden transition weakly allowed. The excitonic coupling (Davydov splitting) can then be measured between the S0 → S1 and S0 → S2 vibrationless bands. We discuss the mass-specific excitonic spectra of five H-bonded dimers that are supersonically cooled to a few K and investigated using two-color resonant two-photon ionization spectroscopy. The excitonic splittings Δcalc predicted by ab initio methods are 5-25 times larger than the experimental excitonic splittings Δexp. The purely electronic ab initio splittings need to be reduced ("quenched"), reflecting the coupling of the electronic transition to the optically active vibrations of the monomers. The so-called quenching factors F < 1 can be determined from experiment (Fexp) and/or calculation (Fcalc). The vibronically quenched splittings F·Δcalc are found to nicely reproduce the experimental exciton splittings. This journal is
... Benzoic acid (BZA) forms a doubly O-H· · · O hydrogen-bonded centrosymmetric (C 2h ) dimer, (BZA) 2 , both in molecular crystals [11][12][13] and in the gas phase, see Figure 1(a). [14][15][16][17][18][19][20][21][22][23] The two carboxyl protons exchange rapidly across the two OH· · · O hydrogen bonds and the self-tautomerism, the height of the double proton-transfer barrier and the associated quantum tunneling effects of (BZA) 2 have been at the focus of many investigations. [11][12][13][14][15][16][17][22][23][24][25][26][27][28][29][30] The mechanistic details have been studied by nuclear magnetic resonance, infrared and ultraviolet (UV) spectroscopies, by X-ray and neutron diffraction techniques and by calculations. ...
... [14][15][16][17][18][19][20][21][22][23] The two carboxyl protons exchange rapidly across the two OH· · · O hydrogen bonds and the self-tautomerism, the height of the double proton-transfer barrier and the associated quantum tunneling effects of (BZA) 2 have been at the focus of many investigations. [11][12][13][14][15][16][17][22][23][24][25][26][27][28][29][30] The mechanistic details have been studied by nuclear magnetic resonance, infrared and ultraviolet (UV) spectroscopies, by X-ray and neutron diffraction techniques and by calculations. [24][25][26][27][28]30,31 In contrast, the coherent electronic excitation transfer in (BZA) 2 , which results in an excitonic splitting between the S 1 and S 2 states, is not as well understood. ...
... Poeltl and McVey measured laser-induced fluorescence (LIF) excitation and emission spectra of supersonic jet-cooled (BZA) 2 at ∼2 cm −1 resolution, but did not obtain additional information on the excitonic coupling. 14,15 High-resolution jet-spectroscopic LIF measurements at 0.008 cm −1 resolution by Meerts and co-workers 22,23 have established that the symmetry of ground-state (BZA) 2 is C 2h , which is lowered to C s in the excited state. These authors also determined the S 0 and S 1 state rotational constants for several isotopomers, and concluded that the BZA· · · BZA distance increases by 0.02−0.03Å in the excited state. ...
The benzoic acid dimer, (BZA)(2), is a paradigmatic symmetric hydrogen bonded dimer with two strong antiparallel hydrogen bonds. The excitonic S(1)/S(2) state splitting and coherent electronic energy transfer within supersonically cooled (BZA)(2) and its (13)C-, d(1) -, d(2) -, and (13)C/d(1) - isotopomers have been investigated by mass-resolved two-color resonant two-photon ionization spectroscopy. The (BZA)(2)-(h - h) and (BZA)(2)-(d - d) dimers are C(2h) symmetric, hence only the S(2) ← S(0) transition can be observed, the S(1) ← S(0) transition being strictly electric-dipole forbidden. A single (12)C/(13)C or H/D isotopic substitution reduces the symmetry of the dimer to C(s), so that the isotopic heterodimers (BZA)(2) - (13)C, (BZA)(2) -(h - d), (BZA)(2) -(h(13)C-d), and (BZA)(2) -(h - d(13)C) show both S(1) ← S(0) and S(2) ← S(0) bands. The S(1)/S(2) exciton splitting inferred is Δ(exc) = 0.94 ± 0.1 cm(-1). This is the smallest splitting observed so far for any H-bonded gas-phase dimer. Additional isotope-dependent contributions to the splittings, Δ(iso), arise from the change of the zero-point vibrational energy upon electronic excitation and range from Δ(iso) = 3.3 cm(-1) upon (12)C/(13)C substitution to 14.8 cm(-1) for carboxy H/D substitution. The degree of excitonic localization/delocalization can be sensitively measured via the relative intensities of the S(1) ← S(0) and S(2) ← S(0) origin bands; near-complete localization is observed even for a single (12)C/(13)C substitution. The S(1)/ S(2) energy gap of (BZA)(2) is Δ(calc) (exc)=11 cm(-1) when calculated by the approximate second-order perturbation theory (CC2) method. Upon correction for vibronic quenching, this decreases to Δ(vibron) (exc)=2.1 cm(-1) [P. Ottiger et al., J. Chem. Phys. 136, 174308 (2012)], in good agreement with the observed Δ(exc) = 0.94 cm(-1). The observed excitonic splittings can be converted to exciton hopping times τ(exc). For the (BZA)(2)-(h - h) homodimer τ(exc) = 18 ps, which is nearly 40 times shorter than the double proton transfer time of (BZA)(2) in its excited state [Kalkman et al., ChemPhysChem 9, 1788 (2008)]. Thus, the electronic energy transfer is much faster than the proton-transfer in (BZA)(2) (∗).
... Tomioka et al. [20] studied the correlation between the frequencies of intermolecular hydrogen bond vibrations between the fluorescence excitation and dispersed fluorescence spectra and concluded that potentials for such vibrations are affected very little upon electronic excitation. Significant discovery was made by Remmers and et al. [21]. On the basis of their high resolution ultraviolet rotationally resolved excitation spectrum of benzoic acid dimer, they have demonstrated convincingly that the linear and planar (C 2h symmetry) ground state geometry of the dimer is slightly in-plane bent (C s symmetry) upon electronic excitation. ...
... This effect is a vibrational analogue of the vibronic coupling, such as the pseudo-Jahn-Teller effect, occurring in the electronic spectra of symmetric dimers [64]. From the experimental data it has been concluded that in the first excited electronic state benzoic acid dimer is in-plane bent as an effect of localised electronic excitation on one moiety of the dimer [14,18,19,21]. ...
... In the first excited singlet state benzoic acid dimer is in-plane bent [14,19,21]. Such symmetry lowering (from C 2h to C s ) causes that degeneracy is removed and Davydov coupling significantly decreases. ...
Theoretical model for vibrational interactions in the hydrogen-bonded benzoic acid dimer is presented. The model takes into account anharmonic-type couplings between the high-frequency O–H and the low-frequency O
⋯
O stretching vibrations in two hydrogen bonds, resonance interactions between two hydrogen bonds in the dimer, and Fermi resonance between the O–H stretching fundamental and the first overtone of the O–H in-plane bending vibrations. The model is used for theoretical simulation of the O–H stretching IR absorption bands of benzoic acid dimers in the gas phase in the first excited singlet state.
Ab initio
CIS and CIS(D)/CIS/6-311++G(d,p) calculations have been carried out in the à state of tropolone. The grids of potential energy surfaces along the coordinates of the tunneling vibration and the low-frequency coupled vibration have been calculated. Two-dimensional model potentials have been fitted to the calculated potential energy surfaces. The tunneling splittings for vibrationally excited states have been calculated and compared with the available experimental data. The model potential energy surfaces give good estimation of the tunneling splittings in the vibrationally ground and excited states of tropolone, and explain monotonic decrease in tunneling splittings with the excitation of low-frequency out-of-plane modes and increase of the tunneling splittings with the excitation of low-frequency planar modes.
... The proton-transfer dynamics in benzoic acid has been studied by various methods, including quasi-elastic neutron scattering [37], ultraviolet [40], or infrared and Raman spectroscopy [38]. Especially the OH stretching band at around 2500 cm À1 has been observed to be influenced significantly by the proton transfer. ...
Since the introduction of ultra-fast laser techniques for the generation and detection of broadband terahertz pulses, terahertz time-domain spectroscopy has become a versatile tool for vibrational spectroscopy of molecular systems in the far-infrared. Due to their highly collective and delocalized character vibrational modes in this part of the spectrum are highly sensitive to molecular structure and arrangement within a molecular crystal. Here we utilize this sensitivity to differentiate between the enantiopure amino acid l-cysteine and its racemic crystalline dl-form. Using terahertz time-domain spectroscopy we are able to observe temperature induced solid-state phase transitions in polycrystalline dl-cysteine, as well as in polycrystalline benzoic acid. The dynamics of the transitions is studied by tracing the temperature dependency of spectral features that are assigned to certain conformational phases.
... Many publications have raised the question if the electronic excitation in symmetrically bound homodimers of aromatic compounds is localized in one of the monomer moieties or is completely delocalized over both monomer moieties. Prototypes of these symmetrical dimers are the benzoic acid dimer investigated by Poeltl and McVey (1984) and by Remmers et al. (2000), the salicylic acid dimer (Yahagi et al. 2001), the 2-pyridone dimer (Held andPratt 1992, Müller et al. 2002), the o-cyanophenol dimer (Lahmani et al. 2002) and the benzonitrile dimer (Schmitt, Böhm, Siegert, van Beek and Meerts 2006). While for the 7-azaindole dimer and the 2-pyridone dimer delocalized excitation is found, the benzoic acid dimer, the fluorobenzoic acid dimer and the o-cyanophenol dimer show a local excitation in only one of the moieties. ...
The usefulness of an evolutionary algorithm (EA) based approach to the automated evaluation of molecular parameters from various kind of spectra is shown. The applicability of the method ranges from rotationally resolved electronic spectroscopy of large molecules to nuclear magnetic resonance (NMR) spectroscopy of molecules, which are partially oriented in an anisotropic liquid-crystalline environment. The application of both the genetic algorithm (GA) and the evolutionary strategy algorithm (ES) approaches for the assignment of complex spectra and the necessity of fitting meta parameters, which are not related to the parameters of the model describing the spectra are discussed. Examples for the possible applications comprise rovibronic spectra of various aromatic water clusters, rovibronic spectra of large hetero- and homo-dimers, rovibrational spectra of the NH stretching vibrations in different tautomers of benzotriazole, and the NMR spectrum of p-bromo-biphenyl dissolved in a nematic crystal.
... From the experimental perspective direct evidence is hard to obtain, as the transfer reaction occurs on the femtosecond (10 -15 s) timescale, requiring the use of multidimensional nonlinear coherent laser spectroscopies. There have been several recent studies on cyclic carboxylic acid dimers [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and other simple systems [10,20], which have given rise to the discovery that the O-H stretching motions are coupled anharmonically to lower frequency vibrational modes, that are in turn responsible for modulating the length of the hydrogen bond. This basic structural mechanism establishes a continuum of potential energy surface (PES) shapes, from the double well at hydrogen bond lengths around 2.6Å, toward a single well at around 2.4Å. ...
In the paper are described studies of the double proton transfer (DPT) processes in the cyclic dimer of acetic acid in the gas phase using Car-Parrinello (CPMD) and path integral molecular dynamics (PIMD). Structures, energies and proton trajectories have been determined. The results show the double proton transfer in 450 K. In the classical dynamics (CPMD) a clear process mechanism can be identified, where asynchronized DPT arises due to coupling between the O-H stretching oscillator and several low energy intermolecular vibrational modes. The DPT mechanism is also asynchronic when quantum tunneling has been allowed in the simulation. It has been found that the calculated values of barrier height for the proton transfer depends very strongly on the used approaches. Barrier received from the free-energy profile at the CPMD level is around 4.5 kcal mol(-1) whereas at the PIMD level is reduced to 1 kcal mol(-1). The nature of bonding in acetic acid dimer and rearrangement of electron density due to the proton movement has been also studied by the topological analysis of Electron Localization Function and Electron Localizability Indicator function.
... Many publications have raised the question if the electronic excitation in symmetrically bound homodimers of aromatic compounds is localized in one of the monomer moieties or is completely delocalized over both monomer moieties. Prototypes of these symmetrical dimers are the benzoic acid dimer investigated by Poeltl and McVey (1984) and by Remmers et al. (2000), the salicylic acid dimer (Yahagi et al. 2001), the 2-pyridone dimer (Held andPratt 1992, Müller et al. 2002), the o-cyanophenol dimer (Lahmani et al. 2002) and the benzonitrile dimer (Schmitt, Böhm, Siegert, van Beek and Meerts 2006). While for the 7-azaindole dimer and the 2-pyridone dimer delocalized excitation is found, the benzoic acid dimer, the fluorobenzoic acid dimer and the o-cyanophenol dimer show a local excitation in only one of the moieties. ...
The usefulness of an evolutionary algorithm (EA) based approach to the automated evaluation of molecular parameters from various kind of spectra is shown. The applicability of the method ranges from rotationally resolved electronic spectroscopy of large molecules to nuclear magnetic resonance (NMR) spectroscopy of molecules, which are partially oriented in an anisotropic liquid-crystalline environment. The application of both the genetic algorithm (GA) and the evolutionary strategy algorithm (ES) approaches for the assignment of complex spectra and the necessity of fitting meta parameters , which are not related to the parameters of the model describing the spectra are discussed. Examples for the possible applications comprise rovibronic spectra of various aromatic water clusters, rovibronic spectra of large hetero-and homo-dimers, rovibra-tional spectra of the NH stretching vibrations in different tautomers of benzotriazole, and the NMR spectrum of p-bromo-biphenyl dissolved in a nematic crystal.
... Over the last two decades a substantial number of experiments have been carried out to investigate the structure and properties of the benzoic acid crystal. The dynamics of double proton transfer of benzoic acid dimers in crystals has been successfully investigated by NMR27282930313233343536, quasi-elastic neutron scattering37383940, inelastic neutron scattering [32,41] , vibrational spectros- copy [42], and 17 O nuclear quadrupole resonance [43], and in the gas phase by laser-induced fluorescence [44] and high resolution UV spectroscopy [45]. It seems to us that it would be interesting to reconstruct the experimental IR spectra of benzoic acid in solids on the basis of the Ratajczak and Yaremko approach and compare them with the results obtained using the Maréchal–Witkowski model [39,46,47]. ...
... It is important to note that several recent studies on cyclic carboxylic acid dimers5152535455 and other simple systems56575859, clearly indicate that the O–H stretching motions are coupled anharmonically to lower frequency vibrational modes, which are in turn responsible for modulating the length of the hydrogen bond. Proton transfer processes in benzoic acid dimer have been extensively studied using NMR, neutron scattering, vibrational spectroscopy and other experimental techniques27282930313233343536373839404142434445. In recent years several theoretical papers have been published on the dynamics of cyclic formic acid dimers606162636465 and other systems666768. ...
The vibrational spectra of polycrystalline benzoic acid (BA) and its deuterated derivative were studied over the wide frequency region 4000–10 cm−1 by IR and Raman methods. A theoretical analysis of the hydrogen bond frequency region and calculations at the B3LYP/6-311++G(2d, 2p) level for the benzoic acid cyclic dimer in the gas phase were made. In order to study the dynamics of proton transfer two formalisms were applied: Car–Parrinello Molecular Dynamics (CPMD) and Path Integrals Molecular Dynamics (PIMD). It was shown that the experimentally observed very broad ν-OH band absorption is the result of complex anharmonic interaction: Fermi resonance between the OH-stretching and bending vibrations and strong interaction of the ν-OH stretching with the low frequency phonons. The theoretical analysis in the framework of such an approach gave a good correlation with experiment. From the CPMD calculations it was confirmed that the O–H⋯O bridge is not rigid, with the O⋯O distance being described by a large amplitude motion. For the benzoic acid dimer we observed stepwise (asynchronous) proton transfer.
