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  • 1
    Electronic Resource
    Electronic Resource
    A molecular beam of tryptophan (1985)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 107 (1985), S. 277-278 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00287a064
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  • 2
    Electronic Resource
    Electronic Resource
    A new six-dimensional analytical potential up to chemically significant energies for the electronic ground state of hydrogen peroxide (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2565-2587 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report calculations of the electronic ground state potential energy surface (PES) of hydrogen peroxide covering, in an almost global fashion, all six internal degrees of freedom by two different ab initio techniques. Density functional theory (DFT) calculations using the Becke 3 parameter Lee–Yang–Parr (B3LYP) hybrid functional and multiconfigurational second order perturbation theory (CASPT2) calculations, both using large basis sets, are performed for a wide range of geometries (8145 DFT and 5310 CASPT2 single-point energies). We use a combined data set of mostly DFT with additional CASPT2 ab initio points and the complete CASPT2 surface to fit a total of four different 6D analytical representations. The resulting potentials contain 70–76 freely adjusted parameters and represent the ground state PES up to 40000 cm−1 above the equilibrium energy with a standard deviation of 100–107 cm−1 without any important artifacts. One of the model surfaces is further empirically refined to match the bond dissociation energy D0 for HOOH→2OH. The potentials are designed for energy regions accessible by vibrational fundamental and overtone spectroscopy including the dissociation channel into hydroxyl radicals. Characteristic properties of the model surfaces are investigated by means of stationary point analyses, torsional barrier heights, harmonic frequencies, low-dimensional cuts and minimum energy paths for dissociation. Overall good agreement with high-level ab initio calculations, especially for the CASPT2 based potentials, is achieved. The drastic change in geometry at intermediate O–O distances, which reflects the transition from covalent to hydrogen bonding, is reproduced quantitatively. We calculate fully 6D anharmonic zero point energies and ground state torsional splittings with the diffusion quantum Monte Carlo method in perfect agreement, within statistical error bars, with experiment for the CASPT2 based potentials. Variational vibrational calculations in the (4+2)D adiabatic approximation yield energy levels and torsional splittings from the ground state up to predissociative states, satisfactorily reproducing the experimental transition wavenumbers. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479534
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  • 3
    Electronic Resource
    Electronic Resource
    Dispersed fluorescence of jet-cooled tryptophan: Excited state conformers and intramolecular exciplex formation (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6945-6951 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dispersed fluorescence of the amino acid tryptophan has been measured in the environment of a cold, supersonic free jet. Analysis of the region of the spectrum near the electronic origin indicates that the electronic excitation spectrum contains features which arise from various ground state conformers of tryptophan, confirming our previous assignment of these features. Under the conditions of our experiment the conformers do not interconvert in the excited state during the fluorescence liftime. Analysis of the dispersed emission spectrum of one conformer reveals broad red-shifted fluorescence which exists even when the electronic origin transition is excited. This broad red-shifted fluorescence is produced by the formation of an intramolecular exciplex involving excited state proton transfer to form a zwitterion. Molecules which do not have the ability to form a zwitterion do not exhibit this behavior, and deuterated trytophan shows broad fluorescence in an amount consistent with a slower proton transfer rate. The significance of these results for understanding the excited state photophysics of tryptophan in solution is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451381
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  • 4
    Electronic Resource
    Electronic Resource
    Local modes of HOOH probed by optical-infrared double resonance (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 865-871 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used an optical-infrared double resonance technique to probe the nature of the eigenstates prepared by 4νOH vibrational overtone excitation in hydrogen peroxide. A visible dye laser excites the 4←0 OH stretch transition and an optical parametric oscillator promotes the molecules above the dissociation threshold by a ΔvOH=2 transition from the 4νOH level. Fixing the overtone excitation laser wavelength and scanning the wavelength of the infrared photon while monitoring the dissociation fragments by laser-induced fluorescence generates an infrared predissociation spectrum of the vibrationally excited molecule that contains information about vibrational state mixing at the 4νOH level. This spectrum indicates that the zeroth-order state that gives oscillator strength to the 4←0 OH stretch transition (i.e., the 4νOH bright state) is almost entirely comprised of a single vibrational eigenstate. Since the bright state is predominantly an OH stretch, the vibrational eigenstate prepared by 4νOH vibrational overtone excitation is well localized on the OH bond. This localization allows us to perform sequential local mode–local mode excitation of the two equivalent OH oscillators in HOOH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461094
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  • 5
    Electronic Resource
    Electronic Resource
    Infrared spectroscopy of vibrationally excited HONO2: Shedding light on the dark states of intramolecular vibrational energy redistribution (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2425-2437 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared predissociation spectroscopy of nitric acid subsequent to vibrational overtone excitation reveals vibrational state mixing of the highly excited levels and probes the character of the coupled dark states. A visible dye laser excites the 4←0 or 5←0 OH stretch transition and an optical parametric oscillator promotes the molecules above the dissociation threshold by a ΔvOH=1 transition from the excited level. Scanning the optical parametric oscillator frequency while monitoring the predissociation products via laser-induced florescence produces an infrared spectrum of the excited molecules. Although the 4νOH vibrational overtone band consists of a single clean rotational contour that falls directly on a Birge–Sponer plot, the infrared transitions from this level indicate that the zeroth-order bright state is extensively mixed. On the average, the zeroth-order bright state is only a minor component of the eigenstates at this energy. The largest collective contribution is from zeroth-order states that have zero quanta of OH stretch.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459866
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  • 6
    Electronic Resource
    Electronic Resource
    The electronic spectrum of the amino acid tryptophan in the gas phase (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 2534-2541 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic spectrum of the amino acid tryptophan has been measured in the environment of a cold, supersonic molecular beam. The resonantly enhanced two-photon ionization spectrum of tryptophan shows some features characteristic of more volatile indole derivitives, however the region of the spectrum near the origin shows distinctive low frequency structure absent from the simpler indole containing molecules. The power dependence of the spectrum reveals features which can be attributed to several conformers of tryptophan in the molecular beam. One of these conformers shows a nearly harmonic 26 cm−1 vibrational progression which does not appear in the spectra of other indole derivitives, and the intensity pattern of this progression indicates that this particular conformer undergoes a significant geometry change upon electronic excitation. The lack of many extensive vibrational progressions in the electronic spectrum indicates that the excited state conformers of tryptophan are similar to those in the ground electronic state. The identification of a small number of stable tryptophan conformers is important for understanding the photophysics of tryptophan in solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450323
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  • 7
    Electronic Resource
    Electronic Resource
    Electronic spectrum of the amino acid tryptophan cooled in a supersonic molecular beam (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 4819-4820 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449009
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  • 8
    Electronic Resource
    Electronic Resource
    Electronic spectroscopy of tryptophan analogs in supersonic jets: 3-Indole acetic acid, 3-indole propionic acid, tryptamine, and N-acetyl tryptophan ethyl ester (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 6539-6549 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic spectroscopy of four different tryptophan analogs, 3-indole acetic acid, 3-indole propionic acid, tryptamine, and N-acetyltryptophan ethyl ester (NATE) has been studied in a supersonic molecular beam using laser-induced fluorescence and resonantly enhanced two-photon ionization. The electronic transition to the lowest excited singlet state occurs at 35 039, 34 965, 34 918, and 34 881±2 cm−1 for 3-indole acetic acid, 3-propionic acid, tryptamine, and NATE, respectively. The relatively small differences in the electronic origin transition frequencies suggests that the lowest excited singlet state for all of these moelcules is the 1Lb state. The spectra reveal that each of these molecules have stable conformers in the gas phase, analogous to our previously reported studies of tryptophan. A low frequency vibrational mode has been observed in 3-indole propionic acid, tryptamine, NATE, and tryptophan which involves motion of the side chain against the indole ring. We have observed that forming a van der Waals complex between tryptamine and a single methanol molecule causes the spectral features due to different conformers of the free molecule to collapse to a single line, suggesting that one particular conformer becomes the most stable species. This emphasizes the importance of including solvent interactions in any attempt to model the behavior of these molecules in solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450705
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