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The change of the 2-pyridone−water cluster (2PYH2O) structure upon electronic excitation is determined by a Franck−Condon analysis of the intensities in the fluorescence emission spectra obtained via excitation of three different vibronic bands as well as a structural fit based on the rotational constants of eight isotopomers that have been reported by Held and Pratt (J. Am. Chem. Soc., 1993, 115, 9708. A total of 93 emission band intensities were fit, together with the changes of rotational constants of 8 isotopomers. The geometry change upon electronic excitation to the state can be described by a strong and unsymmetrical elongation of the hydrogen bonds, a contraction of the OH bond involved in the cyclic cluster arrangement, and an unsymmetrical ring deformation. The resulting geometry changes are interpreted on the basis of ab initio calculations. [ABSTRACT FROM AUTHOR]

We present near- and mid-infrared−UV double resonance spectra of the natural dipeptide H−Pro-Trp−OH. Two conformers are present in the supersonic expansion:  a stretched conformer with fully extended backbone and a folded conformer with an OH···OCpephydrogen bond. Both conformers are stabilized by dispersion interaction between indole ring and peptide backbone and a NHpep/Nprolinecontact. The vibrational and conformational assignment is supported by DFT and MP2 calculations. An adequate description of the energetic order of different conformers requires the explicit inclusion of dispersion and geometry optimization at the MP2 level. We will address the very sensitivity of the observed conformations to the structure of the end groups. [ABSTRACT FROM AUTHOR]

We report the first observation and analysis of rotational band contours of the jet-cooled DNA base adenine for three vibronic bands at 36 062, 36 105, and 36 248 cm-1. The lowest n and states have been labeled with their excited-state vibronic symmetry, and a strong −n vibronic coupling via an out-of-plane vibrational mode has been revealed. The rotational band contours have been recorded by resonant two-photon ionization (R2PI) and analyzed by a genetic algorithm (GA) based fit to obtain the optimum band parameters. The vibronic band at 36 062 cm-1shows dominant c-type character with transition dipole moment (TDM) components a2:b2:c2 0.09:0.17:0.74 and those at 36 105 and 36 248 cm-1show abc-hybrid character with predominantly in-plane TDM components. The band at 36 062 cm-1has been assigned as the n → transition, and the 36 105 cm-1band as the → transition by the symmetry analysis. The band at 36 248 cm-1provides evidence of the strong −n vibronic coupling via an out-of-plane vibrational mode. [ABSTRACT FROM AUTHOR]

Thestructures of the phenol (Ph)–acetylene (A) clusters PhA1,2,3and Ph2A1are assigned on the basisof isomer and mass specific IR–UV double resonance spectroscopyand compared to the structure of the PhA cocrystal. The structuresof the PhA1,2,3clusters are dominated by phenol–acetyleneπ-hydrogen bonds whereas Ph2A1binds viaOH···OH···CC interaction withdominating Ph–Ph hydrogen bond like in the phenol dimer andacetylene attached to the free OH group of the proton acceptor phenol.The macroscopic crystal is a clathrate of phenol with acetylene withhydrogen bridges only between the phenol molecules and not betweenphenol and acetylene.(1) A possible aggregationpathway is proposed in which larger phenol clusters like Ph6are cyclic with no free OH available anymore to which acetylenecould attach as proton acceptor. [ABSTRACT FROM AUTHOR]

The vibronic spectrum of tryptamine has been studied in a molecular beam up to an energy of 930 cm−1above the S0−S1electronic origin. Rotationally resolved electronic spectra reveal a rotation of the transition dipole moment direction from 1Lbto 1Labeginning about 400 cm−1above the 1Lborigin. In this region, vibronic bands which appear as single bands at low resolution contain rotational structure from more than one vibronic transition. The number of these transitions closely tracks the total vibrational state density in the 1Lbelectronic state as a function of internal energy. Dispersed fluorescence spectra show distinct spectroscopic signatures attributable to the 1Lband 1Lacharacter of the mixed excited-state wave functions. The data set is used to extrapolate to a 1Laorigin about 400 cm−1above the 1Lborigin. DFT-MRCI calculations locate a conical intersection between these two states at about 900 cm−1above the Laorigin, whose structure is located along a tuning coordinate which is close to a linear interpolation between the two excited-state geometries. Along the branching coordinate, there is no barrier from 1Lato 1Lb. A two-tier model for the vibronic coupling is proposed. [ABSTRACT FROM AUTHOR]

We reinvestigated the assignment of the three major guanine conformers detected via resonance enhanced two-photon ionization (R2PI) in supersonic expansions and present IR/UV double resonance spectra in the spectral region between 1500 and 1800 cm-1. Comparison with B3LYP/TZVPP and RI-MP2/cc-pVQZ calculations shows that both conformers B and C are 7H-keto tautomers with an imine group in the 2-position. They differ only in the local conformation of the imine group but are otherwise identical. Conformer A is an amino−enol form with the OH group in the trans position. [ABSTRACT FROM AUTHOR]

By using laser-induced heating, we prepared Au−Ag nanoalloys via three different procedures:  (i) mixture of Au nanoparticles and Ag+ ions irradiated by a 532 nm laser, (ii) mixture of Au and Ag nanoparticles irradiated by a 532 nm laser, and (iii) mixture of Au and Ag nanoparticles irradiated by a 355 nm laser. Procedure i is advantageous for the production of spherical alloy nanoparticles; in procedures ii and iii, nanoalloys with a sintered structure have been obtained. The morphology of the obtained nanoalloys depends not only on the laser wavelength but also on the concentration of nanoparticles in the initial mixture. When the total concentration of Ag and Au nanoparticles in the mixture is increased, large-scale interlinked networks have been observed upon laser irradiation. It is expected that this selective heating strategy can be extended to prepare other bi- or multi-metallic nanoalloys. [ABSTRACT FROM AUTHOR]