Size-dependent development of the hydrogen bond network structure in large sized clusters of protonated water, H+(H2O)n (n = 4 to 27), was probed by infrared spectroscopy of OH stretches. Spectral changes with cluster size demonstrate that the chain structures at small sizes (n less, similar 10) develop into two-dimensional net structures (approximately 10 < n < 21), and then into nanometer-scaled cages (n >/= 21).

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OH and CH stretching vibrations of bare phenol, phenol-(H2O)n clusters (n=1–4), and partially deuterated clusters in the S0 state were observed by using IR–UV double resonance and stimulated Raman-UV double resonance spectroscopies. Characteristic spectral features of the OH stretching vibrations of the phenol as well as of the H2O sites were observed, which are directly related to their structures. The cluster structures were investigated by comparing the observed spectra with the calculated ones obtained by the ab initio molecular orbital calculation with (self-consistent field) SCF 6-31G and SCF 6-31G* basis sets given by Watanabe and Iwata. It was found that for the clusters with n≥2, the isomer of ring form hydrogen-bonded structure is most stable and the simulated IR spectra based on the calculated structure showed good agreements with the observed ones. For a particular cluster, which was assigned as an isomer of the n=4 cluster, an anomalous IR spectrum was observed. Two forms of the isomer are proposed with respect to the structure of water moiety: (1) an ‘‘ice’’ structure and (2) an ‘‘ion-pair’’ structure. The relative IR absorption cross sections of each bands were also investigated for the clusters with n=1 to 4. It was found that the IR absorption cross section of the phenolic OH stretching vibration of the n=1 cluster increases by a factor of 6 compared to that of bare phenol and it further increases with the cluster size.

We report UV photodissociation (UVPD) and IR-UV double-resonance spectra of dibenzo-18-crown-6 (DB18C6) complexes with alkali metal ions (Li(+), Na(+), K(+), Rb(+), and Cs(+)) in a cold, 22-pole ion trap. All the complexes show a number of vibronically resolved UV bands in the 36,000-38,000 cm(-1) region. The Li(+) and Na(+) complexes each exhibit two stable conformations in the cold ion trap (as verified by IR-UV double resonance), whereas the K(+), Rb(+), and Cs(+) complexes exist in a single conformation. We analyze the structure of the conformers with the aid of density functional theory (DFT) calculations. In the Li(+) and Na(+) complexes, DB18C6 distorts the ether ring to fit the cavity size to the small diameter of Li(+) and Na(+). In the complexes with K(+), Rb(+), and Cs(+), DB18C6 adopts a boat-type (C(2v)) open conformation. The K(+) ion is captured in the cavity of the open conformer thanks to the optimum matching between the cavity size and the ion diameter. The Rb(+) and Cs(+) ions sit on top of the ether ring because they are too large to enter the cavity of the open conformer. According to time-dependent DFT calculations, complexes that are highly distorted to hold metal ions open the ether ring upon S(1)-S(0) excitation, and this is confirmed by extensive low-frequency progressions in the UVPD spectra.

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Electronic and vibrational spectra of benzo-15-crown-5 (B15C5) and benzo-18-crown-6 (B18C6) complexes with alkali metal ions, M(+)•B15C5 and M(+)•B18C6 (M = Li, Na, K, Rb, and Cs), are measured using UV photodissociation (UVPD) and IR-UV double resonance spectroscopy in a cold, 22-pole ion trap. We determine the structure of conformers with the aid of density functional theory calculations. In the Na(+)•B15C5 and K(+)•B18C6 complexes, the crown ethers open the most and hold the metal ions at the center of the ether ring, demonstrating an optimum matching in size between the cavity of the crown ethers and the metal ions. For smaller ions, the crown ethers deform the ether ring to decrease the distance and increase the interaction between the metal ions and oxygen atoms; the metal ions are completely surrounded by the ether ring. In the case of larger ions, the metal ions are too large to enter the crown cavity and are positioned on it, leaving one of its sides open for further solvation. Thermochemistry data calculated on the basis of the stable conformers of the complexes suggest that the ion selectivity of crown ethers is controlled primarily by the enthalpy change for the complex formation in solution, which depends strongly on the complex structure.

Articles you may be interested inPhotofragment emission yield spectroscopy of acetylene in the D̃ 1 Π u , Ẽ 1 A, and F̃ 1 Σ u + states by vacuum ultraviolet and infrared vacuum ultraviolet double-resonance laser excitations Structures of hydrogen-bonded clusters of benzyl alcohol with water investigated by infrared-ultraviolet double resonance spectroscopy in supersonic jet J. Chem. Phys. 111, 8438 (1999); 10.1063/1.480184 Structures and the vibrational relaxations of size-selected benzonitrile-( H 2 O ) n=1-3 and -( CH 3 OH ) n=1-3 clusters studied by fluorescence detected Raman and infrared spectroscopies J. Chem. Phys. 110, 9504 (1999); 10.1063/1.478915Characterizations of the hydrogen-bond structures of 2-naphthol-( H 2 O ) n (n=0-3 and 5) clusters by infraredultraviolet double-resonance spectroscopy Vibrational spectroscopy of the key functional vibrations of 2-pyridone and its hydrogen-bonded clusters with water, methanol, dioxane, dimethylether, as well as its dimer, has been carried out by using infrared-ultraviolet ͑IR-UV͒ and stimulated Raman-UV double resonance methods combined with fluorescence detection. The characteristic spectral changes upon the cluster formation have been observed for the NH and CvO stretching vibrations of the bare molecule and also for the OH stretching vibrations of the solvent molecules. The cluster structures were investigated by comparing the observed spectra with the simulated ones of the energy-optimized structures obtained by ab-initio molecular orbital calculations. It was found that the ''ring-type'' hydrogen-bonded structure is appropriate for the cluster with water or methanol, while the ''linear-type'' hydrogen-bonded structure is appropriate for the cluster with dioxane or dimethylether. The symmetric form of 2-pyridone dimer was confirmed by the observed spectra, as well as the ab-initio calculation. A clear correlation between the observed frequency shifts of the NH stretching vibrations and the calculated NH¯O hydrogen-bond angles was obtained indicating that the hydrogen-bond angle distortion reduces the local hydrogen-bond strength. Also it was found the blue shifts of the origin bands of the S 1 ←S 0 electronic transition strongly depends on the type of the cluster structures.

We report infrared spectra of hydrogen-bonded phenol−amine clusters, phenol−NH3, −N(CH3)3, −NH(C2H5)2, and −N(C2H5)3, prepared in jet expansions. The OH, NH, and CH stretching fundamentals were studied. Infrared−ultraviolet double-resonance techniques were utilized for vibrational spectroscopy of size-selected clusters. The OH stretch frequencies of the phenol moieties showed extremely large red-shifts from that of bare phenol, reflecting the strong proton affinities of the amines. Moreover, non-proton-transferred structures of the clusters were confirmed. The detailed structure of phenol−NH3 was examined by ab initio calculations, which reproduced the observed infrared spectrum.