Infrared plus vacuum ultraviolet spectroscopy of neutral and ionic methanol monomers and clusters: new experimental results

We present new observations of the infrared (IR) spectrum of neutral methanol and neutral and protonated methanol clusters employing IR plus vacuum ultraviolet (vuv) spectroscopic techniques. The tunable IR light covers the energy ranges of 2500-4500 cm(-1) and 5000-7500 cm(-1). The CH and OH fundamental stretch modes, the OH overtone mode, and combination bands are identified in the vibrational spectrum of supersonic expansion cooled methanol (2500-7500 cm(-1)). Cluster size selected IR plus vuv nonresonant infrared ion-dip infrared spectra of neutral methanol clusters, (CH(3)OH)(n) (n=2,[ellipsis (horizontal)],8), demonstrate that the methanol dimer has free and bonded OH stretch features, while clusters larger than the dimer display only hydrogen bonded OH stretch features. CH stretch mode spectra do not change with cluster size. These results suggest that all clusters larger than the dimer have a cyclic structure with OH groups involved in hydrogen bonding. CH groups are apparently not part of this cyclic binding network. Studies of protonated methanol cluster ions (CH(3)OH)(n)H(+) n=1,[ellipsis (horizontal)],7 are performed by size selected vuv plus IR photodissociation spectroscopy in the OH and CH stretch regions. Energies of the free and hydrogen bonded OH stretches exhibit blueshifts with increasing n, and these two modes converge to approximately 3670 and 3400 cm(-1) at cluster size n=7, respectively.     

IR plus vacuum ultraviolet spectroscopy of neutral and ionic organic acid molecules and clusters: acetic acid

Infrared (IR) vibrational spectroscopy of acetic acid (A) neutral and ionic monomers and clusters, employing vacuum ultraviolet (VUV), 10.5 eV single photon ionization of supersonically expanded and cooled acetic acid samples, is presented and discussed. Molecular and cluster species are identified by time of flight mass spectroscopy: the major mass features observed are A(n)H(+) (n=1-9), ACOOH(+) (VUV ionization) without IR radiation present, and A(+) with both IR and VUV radiation present. The intense feature ACOOH(+) arises from the cleavage of (A)(2) at the beta-CC bond to generate ACOOH(+)+CH(3) following ionization. The vibrational spectrum of monomeric acetic acid (2500-7500 cm(-1)) is measured by nonresonant ionization detected infrared (NRID-IR) spectroscopy. The fundamentals and overtones of the CH and OH stretches and some combination bands are identified in the spectrum. Mass selected IR spectra of neutral and cationic acetic acid clusters are measured in the 2500-3800 cm(-1) range employing nonresonant ionization dip-IR and IR photodissociation (IRPD) spectroscopies, respectively. Characteristic bands observed at approximately 2500-2900 cm(-1) for the cyclic ring dimer are identified and tentatively assigned. For large neutral acetic acid clusters A(n)(n>2), spectra display only hydrogen bonded OH stretch features, while the CH modes (2500-2900 cm(-1)) do not change with cluster size n. The IRPD spectra of protonated (cationic) acetic acid clusters A(n)H(+) (n=1-7) exhibit a blueshift of the free OH stretch with increasing n. These bands finally disappear for n> or =6, and one broad and weak band due to hydrogen bonded OH stretch vibrations at approximately 3350 cm(-1) is detected. These results indicate that at least one OH group is not involved in the hydrogen bonding network for the smaller (n< or =5) A(n)H(+) species. The disappearance of the free OH stretch feature at n> or =6 suggests that closed cyclic structures form for A(n)H(+) for the larger clusters (n> or =6).     

Raman spectra of gas hydrates--differences and analogies to ice 1h and (gas saturated) water

It is generally accepted that Raman spectroscopic investigations of gas hydrates provide vital information regarding the structure of the hydrate, hydrate composition and cage occupancies, but most research is focused on the vibrational spectra of the guest molecules. We show that the shape and position of the Raman signals of the host molecules (H(2)O) also contain useful additional information. In this study, Raman spectra (200-4000 cm(-1)) of (mixed) gas hydrates with variable compositions and different structures are presented. The bands in the OH stretching region (3000-3800 cm(-1)), the O-H bending region (1600-1700 cm(-1)) and the O-O hydrogen bonded stretching region (100-400 cm(-1)) are compared with the corresponding bands in Raman spectra of ice Ih and liquid water. The interpretation of the differences and similarities with respect to the crystal structure and possible interactions between guest and host molecules are presented.     

Correlation between the hydrogen-bond structures and the C=O stretching frequencies of carboxylic acids as studied by density functional theory calculations: theoretical basis for interpretation of infrared bands of carboxylic groups in proteins

Carboxylic groups (COOH) of Asp and Glu side chains often function as key components in enzymatic reactions, and identifying their H-bond structures in the active sites is essential for understanding the reaction mechanisms. In this study, the correlation between the H-bond structures and the C=O stretching (nuC=O) frequencies of COOH groups was studied using density functional theory calculations. The nuC=O frequencies and their shifts upon OH deuteration were calculated for model complexes of acetic acid and propionic acid H bonded at different sites with various compounds. Calculation results together with some experimental data showed that, upon direct H bonding at the C=O group, the nuC=O frequencies downshift from the free value (1770-1780 cm(-1) in an Ar matrix) to 1745-1760 cm(-1), while H bonding at the OH hydrogen induce even larger downshifts to provide the frequencies at 1720-1745 cm(-1). In contrast, when the COH oxygen is H-bonded, the nuC=O frequencies upshift to 1785-1800 cm(-1). In double and multiple H-bond forms, H-bonding effects at individual sites are basically additive, and complexes in which the C=O and the OH hydrogen are simultaneously H bonded exhibit significantly low nuC=O frequencies at 1725-1700 cm(-1), while complexes H bonded at the oxygen of the COH in addition to either at the C=O or the OH hydrogen exhibit medium frequencies of 1740-1765 cm(-1). The nuC=O frequencies linearly correlate with the C=O lengths, which are changed by H bonding at different sites. Upon OH deuteration, all the complexes showed nuC=O downshifts mostly by approximately 10 cm(-1) and in some cases as large as approximately 20 cm(-1), and hence deuteration-induced downshifts can be a good indicator, irrespective of H-bond forms, for assignments of the nuC=O bands of carboxylic groups. The results in this study provide the criteria for determining the H-bond structures of Asp and Glu side chains in proteins using their nuC=O bands in Fourier transform infrared spectra.     

Adsorption of sodium dodecyl sulfate onto clathrate hydrates in the presence of salt

This work presents the effect of NaCl on the adsorption of sodium dodecyl sulfate (SDS) at the cyclopentane (CP) hydrate-water interface. The adsorption isotherms and the SDS solubility in NaCl solutions are obtained using liquid-liquid titrations. The solubility data are determined at typical hydrate forming temperatures (274-287K) to ensure that the adsorption isotherms are obtained within SDS solubility limits in NaCl solutions. The isotherms show L-S (Langmuir-Step) type behaviors with 1mM and 10mM NaCl solutions while L type isotherm is determined for 25mM NaCl solutions due to the low SDS solubility in this salt concentration. Zeta potentials of CP hydrate particles in the aqueous solutions support the shape of the adsorption isotherm with the 1mM NaCl solution. The 1mM NaCl case shows the highest SDS adsorption amount among the cases with 0mM, 10mM, and 25mM NaCl solutions. In this case, the competition for adsorption between Cl(-) and DS(-) is not as strong compared to the 10 and 25mM NaCl cases and the presence of Na(+) ions may reduce the repulsion between DS(-) ions, which results in a higher adsorption of DS(-) ions and enhanced enclathration.     

Computational Study on the Antifreeze Glycoproteins as Inhibitors of Clathrate‐Hydrate Formation

The ability of antifreeze glycoproteins to inhibit clathrate‐hydrate formation is studied using DFT. A 5¹² cavity, dodecahedral (H₂O)₂₀, and the AATA peptide are used to model the inhibitor–clathrate interaction. The presence of AATA in the vicinity of the water cavities not only leads to the formation of complexes, with different peptide/cavity ratios, but also to the deformation of the cavity and to the elongation of several of the hydrogen bonds responsible for keeping the dodecahedral (H₂O)₂₀ together. The complexes are formed through hydrogen bonding between the peptides and the water cavities. The glycoproteins are expected to anchor onto the clathrate surface, blocking the access of new water molecules and preventing the incipient crystals from growing. They are also expected to weaken the clathrate structure. Amide IR bands are associated with the complexes’ formation. They are significantly red‐shifted in the hydrogen‐bonded systems compared to isolated AATA. The amide A band is the most sensitive to hydrogen bonding. In addition a distinctive band around 3100 cm^?1 is proposed for the identification of clathrate–peptide hydrogen‐bonded complexes.     

Vibrational and theoretical study of the 2',6'-dimethoxyflavone cis-formic acid inclusion compound

The FT-infrared and Raman microscopy spectra of the 2',6'-dimethoxyflavone and its 1:1 complex with formic acid in solid state have been recorded and analysed. Some vibrational components appear as specific to the cis-rotamer of formic acid in the crystalline sample, especially the CH group stretching vibration feature. The broad and intense infrared absorption observed in the range 3400-1900 cm(-1) and assigned to the hydrogen bonded OH group stretching vibration exhibits the characteristic ABC structure of strong hydrogen bonded complexes. This ABC pattern corroborates previous X-ray crystallographic data showing that cis-formic acid is strongly hydrogen bonded to the flavonic compound. The inclusion complex is quite unstable and the infrared spectrum clearly shows that formic acid disappears after a period of a few months. In order to get some information on the stability criterions of the intermolecular hydrogen bonded complex, semiempirical AM1 calculations have been investigated. The comparison of the calculated heats of complexation (deltacH) for chelates involving the cis- and trans-conformers of formic acid suggests that the reaction of hydrogen bonding complexation with the cis-rotamer is surely favoured.     

Geometrical behavior of hydrogen bonding patterns in the alpha-dodecyl-omega-hydroxy-tris(oxyethylene)-water system monitored by near infrared spectroscopy

Changes in the geometry of hydrogen bonding patterns in the alpha-dodecyl-omega-hydroxy-tris(oxyethylene) (C(12)E(3))-water system have been investigated by near infrared (NIR) spectroscopy. In the 5,300-4,600 cm(-1) region, the characteristic bands for C(12)E(3) and water can be separately investigated, since the combination bands of the OH stretching and its COH bending of alcohols are observed at 5,000-4,650 cm(-1), whereas the combination bands of the OH stretching and its HOH bending of water, at 5,300-5,000 cm(-1). The NIR result has revealed that the addition of water to C(12)E(3) promotes the formation of the OHcdots, three dots, centeredOHcdots, three dots, centeredO hydrogen bonds.     

Isotope effects in liquid water by infrared spectroscopy. V. A sea of OH4 of C2v symmetry

The two water gas OH stretch vibrations that absorb in the infrared (IR) near 3700 cm(-1) are redshifted to near 3300 cm(-1) upon liquefaction. The bathochromic shift is due to the formation of four H-bonds: two are from the labile hydrogen atoms to neighbors and two are received from neighbors by the oxygen free electron pairs. Therefore, the water oxygen atom is surrounded by four hydrogen atoms, two of these make covalent bonds that make H-bonds and two are oxygen H-bonded. However, these permute at rate in the ps range. When the water molecules are isolated in acetonitrile (MeCN) or acetone (Me(2)CO), only the labile hydrogen atoms make H-bonds with the solvent. The bathochromic shift of the OH stretch bands is then almost 130 cm(-1) with, however, the asymmetric (ν(3)) and symmetric (ν(1)) stretch bands maintained. When more water is added to the solutions, the oxygen lone doublets make H-bonds with the available labile hydrogen atoms from neighboring water molecules. With one bond accepted, the bathochromic shift is further displaced by almost 170 cm(-1). When the second oxygen doublet is filled, another bathochromic shift by almost 100 cm(-1) is observed. The total bathochromic shift is near 400 cm(-1) with a full width at half height of near 400 cm(1). This is the case of pure liquid water. Notwithstanding the shift and the band broadness, the ν(3) and ν(1) band individualities are maintained with, however, added satellite companions that come from the far IR (FIR) absorption. These added to the fundamental bands are responsible for the band broadness and almost featureless shape of the massive OH stretch absorption of liquid water. Comparison of light and heavy water mixture spectra indicates that the OH and OD stretch regions show five different configurations: OH(4); OH(3)D; OH(2)D(2); OHD(3); and OD(4) [J. Chem. Phys. 116, 4626 (2002)]. The comparison of the OH bands of OH(4) with that of OHD(3) indicates that the main component in OHD(3) is ν(OH), whereas in OH(4) two main components are present: ν(3) and ν(1). Similar results are obtained for the OD bands of OD(4) and ODH(3). These results indicate that the C(2) (v) symmetry of H(2)O and D(2)O is preserved in the liquid and aqueous solutions whereas C(s) is that of HDO.     

Nature of water in nacre: a 2D Fourier transform infrared spectroscopic study

In this work, the interactions of aragonite and organic matrix in nacre with water are investigated using two-dimensional (2D) Fourier transform infrared (FTIR) spectroscopy. The 2D-FTIR analysis revealed four bands in the OH stretching region at around 3550, 3445, 3272 and 3074 cm(-1). Two additional bands were found at around 3616 and 3282 cm(-1) after deconvolution of the nacre spectrum. The bands at around 3616 and 3550 cm(-1) are assigned to asymmetric and symmetric OH stretching of partially hydrogen bonded water molecules. The bands at around 3445 and 3272 cm(-1) are assigned to asymmetric and symmetric OH stretching of water molecules fully hydrogen bonded with surrounding water molecules. Presence of above bands in the nacre spectrum suggests that water, in form of clusters, is present in protein matrix and aragonite pores. Water may also hydrogen bond with the organic matrix. The bands observed at 3282 and 3074 cm(-1) are assigned to asymmetric and symmetric OH stretching of water molecules, chemisorbed on surfaces of aragonite platelets. Polarization experiments suggest that H-O-H plane of water molecules is along to c-axis of aragonite platelets.     

Vibrational spectroscopy of size-selected sodium-doped water clusters

The vibrational OH stretch spectra have been measured for Na(H2O)n clusters in the size range from n = 8 to 60. The complete size selection is achieved by coupling the UV radiation of a dye laser below the ionization threshold with the tunable IR radiation of an optical parametric oscillator. The spectra are dominated by intensity peaks around 3400 cm(-1) which we attribute to an increased transition dipole moment of delocalized electrons in this type of doped cluster. Aside from the positions of free (3715 cm(-1)) and double donor (3560 cm(-1)) bonds which are known from pure water clusters, specific transitions are observed at 3640 cm(-1) and in the range of the single donor bonds between 3000 and 3200 cm(-1).     

Ab initio and DFT studies of the vibrational spectra of hydrogen-bonded PhOH...(H2O)4 complexes

The vibrational characteristics (vibrational frequencies and infrared intensities) for the hydrogen-bonded complex of phenol with four water molecules PhOH...(H2O)4 (structure 4A) have been predicted using ab initio and DFT (B3LYP) calculations with 6-31G(d,p) basis set. The changes in the vibrational characteristics from free monomers to a complex have been calculated. The ab initio and B3LYP calculations show that the observed four intense bands at 3299, 3341, 3386 and 3430 cm(-1) can be assigned to the hydrogen-bonded OH stretching vibrations in the complex PhOH...(H2O)4 (4A). The complexation leads to very large red shifts of these vibrations and very strong increase in their IR intensity. The predicted red shifts for these vibrations with B3LYP/6-31G(d,p) calculations are in very good agreement with the experimentally observed. It was established that the phenolic OH stretching vibration is the most sensitive to the hydrogen bonding. The predicted red-shift with the B3LYP/6-31G(d,p) calculations for the most stable ring structure 4A (-590 cm(-1)) is in better agreement with the experimentally observed than the red-shift, predicted with SCF/6-31G(d,p) calculations. The magnitude of the wavenumber shift is indicative of relatively strong OH...H hydrogen-bonded interaction. The complexation between phenol and four water molecules leads to strong increase of the IR intensity of the phenolic OH stretching vibration (up to 38 times).     

Theoretical study of the changes in the vibrational characteristics arising from the hydrogen bonding between Vitamin C (L-ascorbic acid) and H2O

The vibrational characteristics (vibrational frequencies, infrared intensities and Raman activities) for the hydrogen-bonded system of Vitamin C (L-ascorbic acid) with five water molecules have been predicted using ab initio SCF/6-31G(d,p) calculations and DFT (BLYP) calculations with 6-31G(d,p) and 6-31++G(d,p) basis sets. The changes in the vibrational characteristics from free monomers to a complex have been calculated. The ab initio and BLYP calculations show that the complexation between Vitamin C and five water molecules leads to large red shifts of the stretching vibrations for the monomer bonds involved in the hydrogen bonding and very strong increase in their IR intensity. The predicted frequency shifts for the stretching vibrations from Vitamin C taking part in the hydrogen bonding are up to -508 cm(-1). The magnitude of the wavenumber shifts is indicative of relatively strong OH...H hydrogen-bonded interactions. In the same time the IR intensity and Raman activity of these vibrations increase upon complexation. The IR intensity increases dramatically (up to 12 times) and Raman activity increases up to three times. The ab initio and BLYP calculations show, that the symmetric OH vibrations of water molecules are more sensitive to the complexation. The hydrogen bonding leads to very large red shifts of these vibrations and very strong increase in their IR intensity. The asymmetric OH stretching vibrations of water, free from hydrogen bonding are less sensitive to the complexation than the hydrogen-bonded symmetric OH stretching vibrations. The increases of the IR intensities for these vibrations are lower and red shifts are negligible.     

Long-lived interfacial vibrations of water

We have observed long-lived OH-stretch (nu(OH)) excitations (v = 1) in water during ultrafast laser ablation by a mid-infrared pulse tuned to the nu(OH) absorption maximum. The spectrum of excitations is measured using incoherent anti-Stokes Raman spectroscopy. Relative to the equilibrium water spectrum, these excitations evidence a narrowed (100 cm(-1) fwhm) and blue-shifted (3600 cm(-1) peak) transition. The excited-state lifetime is T1 > 200 ps, compared to 0.2 ps in bulk water. In the early stages of the ablation process, the water mean density decreases rapidly, which breaks up the hydrogen bonding. The long-lived species is attributed to nu(OH) excitations on water molecules associated with interfaces, having broken hydrogen bonds which cannot be rapidly reformed as in the liquid state.     

Raman spectroscopic study of the hydrotalcite desautelsite Mg6Mn2CO3(OH)16 x 4H2O

The structure of the hydrotalcite desautelsite Mg6Mn2CO3(OH)16.4H2O has been studied by a combination of Raman and infrared spectroscopy. Three intense Raman bands are observed at 1086, 1062 and 1055 cm(-1). A model based upon the observation of three CO3 stretching vibrations is presented. The CO3 anion may be (a) non-hydrogen bonded, (b) hydrogen bonded to the interlayer water and (c) hydrogen bonded to the brucite-like hydroxyl surface. Two intense bands at 3646 and 3608 cm(-1) are attributed to MgOH and MnOH stretching vibrations. Infrared bands at 3476, 3333, 3165 and 2991 cm(-1) are assigned to water stretching bands. Raman spectroscopy has proven a powerful tool for the study of hydrotalcite minerals.     

The assignment of IR absorption bands due to free hydroxyl groups in cellulose

Interpretation of the IR hydroxyl absorption bands in cellulose has been limited to the inter- and intramolecularly hydrogen-bonded hydroxyl groups in the crystalline form. This paper attempts to assign IR frequencies due to ‘free‘ or non-hydrogen bonded hydroxyl groups by using a curve fitting method. The almost completely methylated cellulose derivatives of tritylcellulose (previously used in related studies) exhibited small IR bands due to hydroxyl groups. The IR bands were assumed to appear under stereohindered conditions and thus resulted in a mixture of bands which included the contribution of free hydroxyl groups. The curve fitting method deconvoluted the IR bands into three bands in the OH stretching region: they were interpreted in terms of free or hydrogen bonded hydroxyl groups. The assignments were confirmed by comparison of an almost completely methylated derivative with partially methylated derivatives having different degrees of substitution. In addition, intramolecular hydrogen bonds involving OH at the C-3, C-2 and C-6 positions were shown to be easily formed, even between extremely small numbers of unsubstituted hydroxyl groups present, and thus cause perturbation of the specific deconvoluted band. This revised version was published online in August 2006 with corrections to the Cover Date.     

Isotope effects in liquid water by infrared spectroscopy. IV. No free OH groups in liquid water

The presence of free OH (OH not H-bonded) in bulk water is a key element for the determination of its molecular structure. The OH covalent bond infrared (IR) absorption is highly sensitive to the molecular environment. For this reason, IR spectroscopy is used for the determination of free OH. A workable definition of this is obtained with methanol (MeOH) in hexane where minute quantities of free OH are present. These absorb at 3654?cm(-1) (a 27?cm(-1) redshift from the gas position) with a full width at half height of 35?cm(-1). The IR spectrum of water between room temperature and 95?°C does not display such a band near 3650?cm(-1). This indicates that we do not see, in the IR spectra, the "free" OH group. From this we conclude that it is not present in liquid water at least down to the 1000 ppm level which is the limit of detectivity of our spectrometer. Other spectroscopic considerations of methanol and water in acetonitrile solutions indicate that weak H-bonds are also not present in liquid water.     

Cholesterol complexes with tri-n-butylphosphate, tri-n-octylamine and cyclohexanone in chlorinated hydrocarbon solvents

The hydrogen bonding interactions of moderately associated cholesterol with tri-n-butylphosphate, tri-n-octylamine and cyclohexanone in dilute solutions of tetrachloromethane, 1,2-dichloroethane and trichloromethane were studied by conventional IR spectroscopy. Information on the stoichiometry of the complexes formed was derived from least squares plots of the linearized expressions of Bjerrum's degree of system formation. The formation constants of the complexes were also determined in this way. The spectra recorded in the OH region from 3100 to 3700 cm-1 were resolved in to the bands of the cholesterol species and the complexes formed. The complexes responsible for the observed bands were recognized from the dependence of their intensity on cholesterol monomer and free base concentration and from their frequency locations. The presence of the complexes B...HO(R) and B...HO(R)...HO(R) with tri-n-butylphosphate and tri-n-octylamine was established in all of the solutions and also for the system cholesterol+cyclohexanone in 1,2-dichloroethane. On the other hand, for cholesterol bonding to cyclohexanone in tetrachloromethane, the model considering complexes with 3:1 and 1:1 stoichiometry seemed the most appropriate.     

IR plus vacuum ultraviolet spectroscopy of neutral and ionic organic acid monomers and clusters: propanoic acid

The vibrational spectrum of molecular propanoic acid, cooled in a supersonic expansion, in the region of 2500 to 7500 cm(-1) is obtained employing infrared plus vacuum ultraviolet nonresonant ionization detected spectroscopy. The fundamental and first overtone of the CH and OH stretch modes of cold propanoic acid molecules can be identified in the spectrum. Propanoic acid neutral and ionic clusters are also studied employing nonresonant ion dip and photodissociation spectroscopic techniques, respectively. For the neutral dimer, a sequence of features observed at ca. 2500-2700 cm(-1) can be assigned as combination bands of low frequency modes with the COH bending overtone; these features characterize the cyclic dimer ring structure. IR spectra of the larger neutral clusters n=3, 4, 5 indicate that they also have cyclic structures in which the OH groups are engaged in the cluster hydrogen bonding network. The CH groups are not involved in this hydrogen bonding structure. Free OH features are observed for the protonated ion clusters (C(2)H(5)COOH)(n)H(+), n=1,...,5, indicating that at least one OH group of these cluster ions is not involved in the cluster hydrogen bonding network. A comparison of the results for four hydrogen bonding neutral and ionic clusters (CH(3)OH, C(2)H(5)OH, CH(3)COOH, and C(2)H(5)COOH) is presented and discussed.     

Infrared plus vacuum ultraviolet spectroscopy of neutral and ionic ethanol monomers and clusters

A high sensitivity spectroscopy is employed to detect vibrational antiitions of ethanol neutrals and ions in a supersonic expansion. The infrared (IR) features located at 3682 and 3667 cm(-1) can be assigned to the OH stretch for the two neutral C(2)H(5)OH conformers, anti and gauche, respectively. Their overtone energies located at 7179 (anti) and 7141 (gauche) cm(-1) are also identified. The OH fundamental stretch for ethanol ions is redshifted around 210 cm(-1), while the CH stretch modes are unchanged for neutral and ionic C(2)H(5)OH at around 2900-3000 cm(-1). The charge on the ethanol ion is apparently localized on the oxygen atom. IR induced photodissociation spectroscopy is applied to the study of neutral and protonated ethanol clusters. Neutral and protonated ethanol cluster vibrations are observed. The CH modes are not perturbed by the clustering process. Neutral clusters display only hydrogen bonded OH features, while the protonated ionic clusters display both hydrogen bonded and non-hydrogen-bonded features. These spectroscopic results are analyzed to obtain qualitative structural information on neutral and ionic ethanol clusters.