The hydrogen bond is the most important of all directional intermolecular interactions. It is operative in determining molecular conformation, molecular aggregation, and the function of a vast number of chemical systems ranging from inorganic to biological. Research into hydrogen bonds experienced a stagnant period in the 1980s, but re-opened around 1990, and has been in rapid development since then. In terms of modern concepts, the hydrogen bond is understood as a very broad phenomenon, and it is accepted that there are open borders to other effects. There are dozens of different types of X-H.A hydrogen bonds that occur commonly in the condensed phases, and in addition there are innumerable less common ones. Dissociation energies span more than two orders of magnitude (about 0.2-40 kcal mol(-1)). Within this range, the nature of the interaction is not constant, but its electrostatic, covalent, and dispersion contributions vary in their relative weights. The hydrogen bond has broad transition regions that merge continuously with the covalent bond, the van der Waals interaction, the ionic interaction, and also the cation-pi interaction. All hydrogen bonds can be considered as incipient proton transfer reactions, and for strong hydrogen bonds, this reaction can be in a very advanced state. In this review, a coherent survey is given on all these matters.

The hydrogen bond in the solid state.

Die Wasserstoffbrucke ist die wichtigste der gerichteten intermolekularen Wechselwirkungen. Sie spielt fur die molekulare Konformation, Aggregation und Funktion einer grosen Anzahl chemischer Systeme, die vom anorganischen bis zum biologischen Sektor reichen, wichtige Rollen. Die Forschung uber Wasserstoffbrucken stagnierte in den 1980er Jahren, wurde um 1990 aber wieder belebt und ist seither in schneller Bewegung. Die Wasserstoffbrucke wird heute als ein sehr breites Phanomen mit offenen Grenzen zu anderen Effekten begriffen. In den kondensierten Phasen gibt es dutzende Arten von haufig vorkommenden X−H⋅⋅⋅A-Wasserstoffbrucken und zusatzlich sehr viele weniger haufige Typen. Die Dissoziationsenergien uberstreichen mehr als zwei Grosenordnungen (etwa 0.2 bis 40 kcal mol−1). Innerhalb dieses Bereiches ist die Natur der Wechselwirkung nicht konstant, sondern ihre elektrostatischen, kovalenten und dispersiven Anteile variieren in ihren relativen Beitragen. Die Wasserstoffbrucke hat breite Ubergangsbereiche zur kovalenten Bindung, zur Van-der-Waals-Wechselwirkung, zur ionischen Wechselwirkung und zur Kation-π-Wechselwirkung. Wasserstoffbrucken konnen als beginnende Protonentransferreaktion aufgefasst werden, und fur starke Wasserstoffbrucken kann diese Reaktion bereits in einem fortgeschrittenen Stadium sein. In diesem Aufsatz wird versucht, einen zusammenhangenden Uberblick uber alle diese Aspekte zu geben.

Die Wasserstoffbrücke im Festkörper

Wettability of porous polydimethylsiloxane surface: morphology study

The technique of molecular beam photofragment translational spectroscopy has been used to study the dissociation of acetone following S1←S0 (248 nm) and S2←S0 (193 nm) excitation. Excitation at 248 nm resulted in the production of CH3 and CH3CO with 14.2±1.0 kcal/mole on average of the available energy appearing as translation of the photofragments. Comparison of the measured 〈ET〉 with values reported at 266 nm suggest that the energy partitioning is dominated by the exit barrier caused by an avoided crossing on the potential energy surface. A substantial fraction (30±4%) of the nascent acetyl radicals from the primary dissociation contain sufficient energy to undergo spontaneous secondary decomposition. From the onset of the truncation of the CH3CO P(ET) a threshold of 17.8±3.0 kcal/mole for the dissociation of the acetyl radical has been determined in agreement with recent results on the photodissociation of acetyl chloride. The translational energy release in the dissociation of CH3CO closely matches t...

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Evidence for stepwise dissociation dynamics in acetone at 248 and 193 nm

The photofragment internal and translational energy distributions resulting from the 193 nm photolysis of acetone have been measured. Vacuum‐ultraviolet laser‐induced fluorescence was used to probe the CO fragment, and multiphoton ionization time‐of‐flight mass spectrometry was used to probe the CH3. A Boltzmann distribution was observed to fit each degree of freedom with the following characteristic temperatures: CO: Tvib =2700 K, Trot =3000 K, Ttrans =3000 K; CH3: Tvib =800 K, Trot =500 K, Ttrans =3500 K. No evidence was found for two distinct CH3 populations, as might be characteristic of a stepwise reaction. Energy partitioning between the fragments was fit well by a simple impulsive model in which the available energy is divided equally between the two dissociating C–C bonds, the two bonds cleaving in rapid succession on a time scale short enough to allow little redistribution of energy into the methyl degrees of freedom.

Photodissociation dynamics of acetone at 193 nm: Photofragment internal and translational energy distributions

The rovibrational state distribution of the nascent NH2(A 2A1) fragments generated by 193.3 nm photodissociation of a room temperature sample of NH3 is determined through an analysis of a major portion (6000–13 000 cm−1) of the NH2(A 2A1→X 2B1) near infrared emission spectrum obtained by time‐resolved Fourier transform infrared emission spectroscopy. The NH2(A) fragments are observed to be formed predominantly in their zero‐point vibrational level, with substantial rotational excitation about their a‐inertial axis up to the limit of the available energy, ∼3150 cm−1, but with little excitation about the other axes. The pattern of this energy disposal is discussed within the framework of existing knowledge regarding the form of the NH3 A state potential energy surface on which the dissociation occurs. The essential features are entirely consistent with a direct carry over, into the fragment, of the out‐of‐plane bending vibrational motion introduced in the parent molecule by the photoexcitation process.

Photodissociation of ammonia at 193.3 nm: Rovibrational state distribution of the NH2(Ã 2A1) fragment

Photofragmentation of acetone at 193 nm is known to produce predominantly two methyl radicals and a CO molecule. Infrared emission is collected for the CO fragment at time delays of 6-30 ..mu..s after the exciting laser pulse by a time-resolved Fourier transform spectrometer. High-resolution vibration-rotation spectra are obtained both under collision-free and rotationally relaxed conditions. The observed vibrational distribution is, for v = 1/2/3, 0.73 /plus minus/ 0.04/0.23 /plus minus/ 0.02/0.04 /plus minus/ 0.01. This distribution fits a temperature of /approximately/ 2030/sub /minus/430//sup +730/ K, in approximate agreement with previous low-resolution results from this laboratory. The observed rotational distribution is highly excited, approximating a temperature of 3360/sub /minus/800//sup +1540/ K. Both the vibrational and rotational distributions can be successfully modeled by using a pure impulsive mechanism for the fragmentation of an initial bent acetyl fragment. Thus, the observed distribution supports previous arguments that the dissociation occurs by a two-step fragmentation mechanism following single-photon excitation.

Photofragmentation of acetone at 193 nm: rotational- and vibrational-state distributions of the carbon monoxide fragment by time-resolved FTIR emission spectroscopy

The atom-radical reaction Cl + C[sub 2]H[sub 5] [yields] HCl(v) + C[sub 2]H[sub 4] is studied using laser flash photolysis, time-resolved Fourier transform infrared emission spectroscopy and broad band infrared chemiluminescence. The Cl atoms and ethyl radicals are produced from a number of different precursors using one or two lasers. The initial HCl vibrational distribution is determined to be HCl (v=1/2/3/4=0.39 [plus minus] 0.04/0.29 [plus minus] 0.03/0.22 [plus minus] 0.02/0.10 [plus minus] 0.02). The vibrational distribution is characteristic of an addition-elimination mechanism and can be reproduced using modified statistical theories of energy partitioning within the [C[sub 2]H[sub 5]Cl]z[double dagger] intermediate. The time evolution of the HCl(v=4) emission is used to estimate a rate coefficient for this reaction of (3.0 [plus minus] 1.0) x 10[sup [minus]10] cm[sup 3] molecule[sup [minus]1] s[sup [minus]1]. 39 refs., 8 figs., 6 tabs.

A laser flash photolysis, time-resolved Fourier transform infrared emission study of the reaction monochlorine + ethyl .fwdarw. hydrogen chloride(v) + ethene

FTIR spectra of the matrix‐isolated monomeric and complexed H2S in solid O2 at 13 K have been obtained at various matrix: solute ratios (M/S) in order to identify the ν3 absorption of the monomer. The ν1 absorption of the monomer was too weak to be seen at high dilutions, M/S∼4000 and 8000. The previous assignments of the monomer ν1 absorption in Ar and N2 are questioned. The satellite peaks appearing at low values of (M/S) are assigned to (H2S)2. The observed H‐bonding dimer frequency, −50 cm−1 from v3, is comparable to the value calculated using second‐order Mo/ller‐Plesset perturbation theory. Frequencies calculated at the Hartree–Fock level for H2S dimer are essentially unchanged from those in the monomer.

Infrared spectra of matrix‐isolated monomeric and dimeric hydrogen sulfide in solid O2

Photofragmentation of Acetone at 193 nm: Rotational- and Vibrational-State Distributions of the CO Fragment by Time-Resolved FTIR Emission Spectroscopy.

Eric L. Woodbridge

Papers

Photodissociation of ammonia at 193.3 nm: Rovibrational state distribution of the NH2(Ã 2A1) fragment

Photofragmentation of acetone at 193 nm: rotational- and vibrational-state distributions of the carbon monoxide fragment by time-resolved FTIR emission spectroscopy

A laser flash photolysis, time-resolved Fourier transform infrared emission study of the reaction monochlorine + ethyl .fwdarw. hydrogen chloride(v) + ethene

Infrared spectra of matrix‐isolated monomeric and dimeric hydrogen sulfide in solid O2

Photofragmentation of Acetone at 193 nm: Rotational- and Vibrational-State Distributions of the CO Fragment by Time-Resolved FTIR Emission Spectroscopy.