Unraveling anharmonic effects in the vibrational predissociation spectra of H5O2(+) and its deuterated analogues

The nature of anharmonic couplings in the H(5)O(2)(+) "Zundel" ion and its deuterated isotopologues is investigated through comparison of their measured and calculated vibrational spectra. This follows a recent study in which we reported spectra for H(5)O(2)(+), D(5)O(2)(+), and D(4)HO(2)(+) from ～600 to 4000 cm(-1), as well as H(4)DO(2)(+) in the OH and OD stretching regions [ J. Phys. Chem. B 2008 , 112 , 321 ]. While the assignments of the higher-energy transitions associated with the fundamentals of the exterior OH and OD motions are relatively straightforward, difficulties arise in the assignment of the lower-frequency regions that involve displacement of the bridging proton, especially for the isotopically mixed species. Here we revisit the Ar-tagged isotopomers, and report the low energy action spectrum of H(4)DO(2)(+) for the first time, as well as present significantly improved spectra for the D(4)HO(2)(+) and D(5)O(2)(+) systems. Band assignments are clarified in several cases using IR-IR hole-burning. We then investigate the physical origin of the anharmonic effects encoded in these spectra using a recently developed technique in which the anharmonic frequencies and intensities of transitions (involving up to two quanta of excitation) are evaluated using the ground state probability amplitudes [ J. Phys. Chem. A 2009 , 113 , 7346 ] obtained from diffusion Monte Carlo simulations. This approach has the advantage that it is applicable to low-symmetry systems [such as (HDO)H(+)(OH(2))] that are not readily addressed using highly accurate methods such as the multiconfigurational time-dependent Hartree (MCTDH) approach. Moreover, it naturally accommodates an intuitive evaluation of the types of motion that contribute oscillator strength in the various regions of the spectrum, even when the wave function is intrinsically not separable as a product of low-dimensional approximate solutions. Spectra for H(5)O(2)(+), D(5)O(2)(+), H(4)DO(2)(+), and D(4)HO(2)(+) that are calculated by this approach are shown to be in excellent agreement with the measured spectra for these species, leading to reassignments of two of the bands in the intramolecular bending region of D(4)HO(2)(+).     

The vibrational predissociation spectra of the H5O2 +RGn(RG = Ar,Ne) clusters: correlation of the solvent perturbations in the free OH and shared proton transitions of the Zundel ion

Predissociation spectra of the H(5)O(2) (+)RG(n)(RG = Ar,Ne) cluster ions are reported in energy regions corresponding to both the OH stretching (3350-3850 cm(-1)) and shared proton (850-1950 cm(-1)) vibrations. The two free OH stretching bands displayed by the Ne complex are quite close to the band origins identified earlier in bare H(5)O(2) (+) [L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee, J. Chem. Phys. 91, 7319 (1989)], indicating that the symmetrical H(5)O(2) (+) "Zundel" ion remains largely intact in H(5)O(2) (+)Ne. The low-energy spectrum of the Ne complex is simpler than that observed previously for H(5)O(2) (+)Ar, and is dominated by two sharp transitions at 928 and 1047 cm(-1), with a weaker feature at 1763 cm(-1). The H(5)O(2) (+)Ar(n),n = 1-5 spectra generally exhibit complex band structures reflecting solvent-induced symmetry breaking of the Zundel core ion. The extent of solvent perturbation is evaluated with electronic structure calculations, which predict that the rare gas atoms should attach to the spectator OH groups of H(5)O(2) (+) rather than to the shared proton. In the asymmetric complexes, the shared proton resides closer to the more heavily solvated water molecule, leading to redshifts in the rare gas atom-solvated OH stretches and to blueshifts in the shared proton vibrations. The experimental spectra are compared with recent full-dimensional vibrational calculations (diffusion Monte Carlo and multimode/vibrational configuration interaction) on H(5)O(2) (+). These results are consistent with assignment of the strong low-energy bands in the H(5)O(2) (+)Ne spectrum to the vibration of the shared proton mostly along the O-O axis, with the 1763 cm(-1) band traced primarily to the out-of-phase, intramolecular bending vibrations of the two water molecules.     

Quantum dynamics of Ne-Br2 vibrational predissociation: the role of continuum resonances as doorway states

Wave-packet simulations of the Ne-Br2(B,upsilon') vibrational predissociation dynamics in the range upsilon' = 16-29 are reported. The aim is to interpret recent time-dependent pump-probe experiments [Cabrera et al., J. Chem. Phys. 123, 054311 (2005)]. Good agreement is found between the calculated and the experimental lifetimes corresponding to decay of the Ne-Br2(B,upsilon') initial state and to appearance of Br2(B,upsilon相似文献   

Shock tube studies of the N2O/Ar and N2O/H2/Ar systems

N₂O decay has been monitored via infrared emission for a series of mixtures containing N₂O/Ar and N₂O/H₂/Ar. These mixtures were studied behind reflected shock waves in the temperature interval of 1950–3075°K with total concentrations ranging from 1.2 to 2.5 × 10¹⁸ molec/cm³. In all cases the N₂O decayed exponentially, and a rate constant k_obs was obtained. Runs without added H₂ could be described by the following Arrhenius parameters: log A = ?9.72 ± 0.08 (in units of cm³/molec · sec) and E_A = 203.5 ± 3.6 kJ/mole. Addition of 0.01% and 0.1% H₂ was observed to increase the decay rate; the largest increase occurred between 2250 and 2500°K with 0.1% H₂, where k_obs doubled. Mixtures with no added H₂ were analyzed by numerical integration of the following reactions: Quantitative agreement between calculations and observations were obtained with both high and low choices for k₂ and k₃. The additional reactions were included in the analysis of the mixtures containing H₂. Here agreement was obtained only when low values were assigned to k₂ and k₃. The combinations of k₁ ← k₃ which agreed with all the data were k₁ = 3.25 × 10^?10 exp (?215 kJ/RT) and k₂ = k₃ = 1.91 × 10^?11 exp (-105 kJ/RT).     

Theoretical study on structures and vibrational spectra of M+(H2O)Ar (M = Cu,Ag, Au)

A theoretical study on the structures and vibrational spectra of M⁺(H₂O)Ar_0‐1 (M = Cu, Ag, Au) complexes was performed using ab initio method. Geometrical structures, binding energies (BEs), OH stretching vibrational frequencies, and infrared (IR) absorption intensities are investigated in detail for various isomers with Ar atom bound to different binding sites of M⁺(H₂O). CCSD(T) calculations predict that BEs are 14.5, 7.5, and 14.4 kcal/mol for Ar atom bound to the noble metal ion in M⁺(H₂O)Ar (M = Cu, Ag, Au) complexes, respectively, and the corresponding values have been computed to be 1.5, 1.3, and 2.1 kcal/mol when Ar atom attaches to a H atom of water molecule. The former structure is predicted to be more stable than the latter structure. Moreover, when compared with the M⁺(H₂O) species, tagging Ar atom to metal cation yields a minor perturbation on the IR spectra, whereas binding Ar atom to an OH site leads to a large redshift in OH stretching vibrations. The relationships between isomers and vibrational spectra are discussed. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

H/D isotopic recognition in hydrogen bonded systems: H/D isotopic self-organization effects in the IR spectra of the hydrogen bond in 2-methylimidazole crystals

Polarized IR spectra of H12(3)45 2-methylimidazole and of its H1D2(3)45, D1H2(3)45 and D12(3)45 deuterium derivative crystals are reported and interpreted within the limits of the "strong-coupling" theory. The spectra interpretation facilitated the recognition of the H/D isotopic "self-organization" phenomenon, which depends on a non-random distribution of protons and deuterons in the lattices of isotopically diluted crystal samples. The H/D isotopic "self-organization" mechanism engaged all four hydrogen bonds from each unit cell. These effects basically resulted from the dynamical co-operative interactions involving adjacent hydrogen bonds in each hydrogen bond chain. A weaker exciton coupling involved the closely spaced hydrogen bonds; each belonging to a different chain of associated 2-methylimidazole molecules. The high intensity of the narrow band at ca. 1880cm(-1) was interpreted as the result of coupling between the γ(N-H?N) proton bending "out of plane" vibration overtone and the ν(N-H) proton stretching vibration.     

Relaxation of H2O from its /04>- vibrational state in collisions with H2O, Ar, H2, N2, and O2

We report rate coefficients at 293 K for the collisional relaxation of H2O molecules from the highly excited /04>(+/-) vibrational states in collisions with H2O, Ar, H2, N2, and O2. In our experiments, the mid R:04(-) state is populated by direct absorption of radiation from a pulsed dye laser tuned to approximately 719 nm. Evolution of the population in the (/04>(+/-)) levels is observed using the combination of a frequency-quadrupled Nd:YAG laser, which selectively photolyses H2O(/04>(+/-)), and a frequency-doubled dye laser, which observes the OH(v=0) produced by photodissociation via laser-induced fluorescence. The delay between the pulse from the pump laser and those from the photolysis and probe lasers was systematically varied to generate kinetic decays. The rate coefficients for relaxation of H2O(/04>(+/-)) obtained from these experiments, in units of cm3 molecule(-1) s(-1), are: k(H2O)=(4.1+/-1.2) x 10(-10), k(Ar)=(4.9+/-1.1) x 10(-12), k(H2)=(6.8+/-1.1) x 10(-12), k(N2)=(7.7+/-1.5) x 10(-12), k(O2)=(6.7+/-1.4) x 10(-12). The implications of these results for our previous reports of rate constants for the removal of H2O molecules in selected vibrational states by collisions with H atoms (P. W. Barnes et al., Faraday Discuss. Chem. Soc. 113, 167 (1999) and P. W. Barnes et al., J. Chem. Phys. 115, 4586 (2001).) are fully discussed.     

Fundamental excitations of the shared proton in the H3O2- and H5O2+ complexes

We exploit recent advances in argon predissociation spectroscopy to record the spectroscopic signature of the shared proton oscillations in the H3O2- system and compare the resulting spectrum with that of the H5O2+ ion taken under similar conditions. Very intense 1 <-- 0 transitions are observed below 1100 cm(-1) in both cases and are surprisingly sharp, with the 697 cm(-1) transition in H3O2- being among the lowest in energy of any shared proton system measured to date. The assignments of the three fundamental transitions associated with the three-dimensional confinement of the shared proton in H3O2- are carried out with full-dimensional (DMC) calculations to treat this strongly anharmonic vibrational problem.     

Tetracyanonickelate compounds as sorptive materials and the substitution of their H2O content by D2O

The compounds NiNi(CN)₄·3,5H₂O and Ni(NH₃)₂Ni(CN)₄·H₂O have been studied to examine the possibility of substituting their H₂O or NH₃ content by D₂O. Contact with D₂O was performed after heating the compounds to several temperatures. Depending on the degree of decomposition of the original compounds different ranges of substitution were possible. In such manner the compounds NiNi(CN)₄·3,5D₂O, NiNi(CN)₄·5D₂O, Ni(NH₃)₂Ni(CN)₄·D₂O, and Ni(D₂O)₂Ni(CN)₄·D₂O were prepared and thermally they were less stable than the original ones. The substitution by D₂O is in agreement with the sorptive properties of the original tetracyanonickelate against different organic compounds using GC, since these could substitute the guest component and sometimes also the ligands during their decomposition.     

The thermal dehydration of Sr(HCOO)2·2(H,D)2O. Influence of the isotopic substitution on the kinetics

The kinetics of thermal dehydration of Sr(HCOO)₂·2(H, D)₂O were investigated using a dynamic thermogravimetric technique. Differences were found when the hydrogen was partially substituted by deuterium. These differences were explained by means of a microscopic approach based on the static and dynamic microscopic properties.

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Zusammenfassung Die Kinetik der thermischen Dehydratisierung von Sr(HCOO)₂·2(H, D)₂O wurde mittels dynamischer Thermogravimetrie untersucht. Bei partieller Substitution von Wasserstoff durch Deuterium wurden Unterschiede gefunden, die durch eine auf den statischen und dynamischen mikroskopischen Eigenschaften beruhende Betrachtungsweise erklärt werden.

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Sr(HCOO)₂ · 2(H, D)₂O. , .

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The authors whish to thank Dr. J. M. Pastor for valuable discussions, and Prof. O. Garcia of the Instituto de Quimica Inorgánica Elhuyar (C.S.I.C.) for the use of the experimental devices.     

Rydberg series in the absorption spectra of H2O and D2O in the vacuum ultraviolet

The photoabsorption cross section of molecular H₂O and D₂O has been determined in the range from hν = 10eV to 20 eV with 0.03 Å resolution. A refined analysis of the Rydberg series including the rotational line shapes of several bands to locate the band origins and a comparison with recent ab initio calculations is given. In the region of continuous absorption we have assigned a p-type and an s-type Rydberg series leading to the ²A₁ and the ²B₂ state respectively with quantum defects δ ≈ 0.75 and δ ≈ 1.36.     

The vibrational spectra of the crystalline tripotassium hydrogen pyrophosphates K3HP2O7.3H2O and K3HP2O7

The i.r. and Raman spectra of tripotassium hydrogen pyrophosphate trihydrate (KHPT), K₃HP₂O₇.3H₂O, and anhydrous tripotassium hydrogen pyrophosphate (KHPA), K₃HP₂O₇, and of their deuterated analogues have been studied between 4000 and 200 cm⁻¹. All the bands observed have been assigned. The spectroscopic study shows HP₂O³⁻₇ anions linked by hydrogen bonds, forming infinite chains. The water hydration molecules are determinants of the structure, and after the dehydration one could note an upward shift of the vOH stretching mode and then a weakening of the hydrogen bond.     

Polarization IR spectra of hydrogen bonded pyrazole crystals: self-organization effects in proton and deuteron mixture systems. Long-range H/D isotopic effects

This paper deals with experimental studies of the polarization IR spectra of solid-state pyrazole H1345, as well as of its H1D345, D1H345 and D1345 deuterium derivatives. Spectra were measured for the vN-H and vN-D band frequency ranges at temperatures of 298 and 77 K. The spectra were found to strongly change their intensity distribution and their polarization properties with the decrease of temperature. These effects were ascribed to some temperature-induced conformational changes in the hydrogen bond lattices. The studies reported allowed the finding of new kind of isotopic effects H/D in the open-chain hydrogen bond systems, i.e. the self-organization effects. It was found that the spectrally active aggregates of hydrogen bonds remain unchanged despite the growing isotope H/D exchange rate. This statement was supported by analysis of the residual polarized vN-H and vN-D band properties, measured for the isotopically diluted crystalline samples. Analysis of the band shapes of the four hydrogen isotope derivative crystals proved the existence of another kind of H/D isotopic effect, i.e. the long-range isotopic effect. It depends on an influence of the pyrazole ring hydrogen atoms onto the vN-H and vN-D band widths and onto the band fine structures.     

Infrared spectroscopy and effective modes analysis of the protonated water dimer H+(H2O)2 at room temperature under H/D substitution

We study the vibrational properties of the protonated water dimer and its deuterated forms at room temperature. Molecular dynamics simulations within the empirical valence bond (EVB) model are used to generate the vibrational spectra that are interpreted using the effective modes analysis (EMA). Quantum effects are taken into account through an effective parametrization of the EVB model. EMA allows for the assignment of the bands in the 1000 - 2000?cm(-1) region of the protonated water dimer from the molecular dynamics trajectory. It is then found that although this system is very anharmonic the two main bands in this spectral region arise from a linear coupling between the asymmetric OH(+)O stretch and asymmetric bend of the two water molecules. This mixing explains the simulated band shifts upon isotopic substitution of the central proton or of the hydrogens of the two water molecules.     

Raman spectroscopy study of species responsible for the fast proton conductivity in H2Sb4O11.3H2O

The Raman spectroscopy study of crystallized antimonic acid trihydrate powders in the 20–4000 cm⁻¹ confirme the explicit formula : (H₃O⁺)_2−x[Sb₄O_11−xOH_x]^−(2−x).(3+x−2)H₂O. Furthermore it emphasizes the presence of hydrogen bonds between either the SbOSb bridge and H₃O⁺ or the protonated Sb(OH)Sb bridge and H₂O.     

Secondary isotope effects in the mass spectra of C2D5OC2H5 and CD3CH2OC2H5

Secondary isotope effects were examined in the loss of methyl from the molecular ions of C₂D₅OC₂H₅ and CD₃CH₂OC₂H₅ for ion source processes and collisional activation (CA) processes. In the ion source loss of CH₃ was slightly favored over loss of CD₃, but in CA the CH₃ loss was favored to a much larger extent than expected. A possible explanation is given which invokes an energy distribution function peaked near the appearance energy for the methyl loss process.