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  • 1
    Electronic Resource
    Electronic Resource
    Structure and dynamics of 9-ethylfluorene-Arn van der Waals complexes (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3389-3397 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The neutral S1 excited state and the ion ground state of 9-ethylfluorene-Arn van der Waals complexes have been studied for n=1–3. Resonance enhanced multiphoton ionization spectroscopy of the S1 state of the argon clusters reveals multiple isomeric structures for each of the cluster sizes studies coupled with the two monomer conformations. The n=1 cluster shows three isomers, one of the symmetric 9-ethylfluorene and two of the unsymmetric. The n=2 clusters has four possible isomers all of which are assigned to a (1|1) conformation, although each represents a unique structure with different argon binding sites. The n=3 cluster collapses down to two dominate isomers, one for each conformation of the parent. Mass analyzed threshold ionization (MATI) spectroscopy was used to investigate the ion, as well as assisting in isomer assignment of the S1 spectrum. IVR and dissociation of the argon complexes have also been studied with MATI spectroscopy. Ab initio calculations are used to determine the binding energy for all conformers and isomers of the n=1 complex. These values are in excellent agreement with the experimentally bracketed values, and prove useful in isomer assignments. Redistribution of the 208 cm−1 band of the n=2 symmetric conformation shows dynamics suggesting interconversion of all isomers to a new unassigned structure. Preferential dissociation of the argon located on the ethyl chain side of the sym-9-ethylfluorene-Ar2 complex is observed in both isomers. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478205
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  • 2
    Electronic Resource
    Electronic Resource
    Conformational energy and dynamics of 9-ethylfluorene (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3378-3388 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The S1 excited state and cation ground state of jet cooled 9-ethylfluorene have been studied experimentally using resonant enhanced multiphoton ionization and zero electron kinetic energy (ZEKE) photoelectron spectroscopy. The spectroscopy has identified two conformations of the ethyl chain which are labeled symmetric and unsymmetric both of which exist in the supersonic expansion. Density functional quantum chemical calculations are used to calculate the ground state and cation energies of each conformer as well as the barrier to conformer interconversion via a bond rotation. Dynamics on the S1 surface are measured using picosecond and nanosecond ZEKE photoelectron spectroscopy. Fast irreversible vibrational redistribution is measured at energies ≥990 cm−1 and the ZEKE spectra are shown to have a unique signature for each of the two isomers. Picosecond and nanosecond ZEKE spectroscopy are used to search for conformer interconversion but even at the highest energy probed (2648 cm−1) no evidence is seen for a dynamic barrier crossing. Statistical density of states calculations are used to predict the relative populations of each conformer expected as a function of excess energy as well as related Rice–Ramsperger–Kassel–Marcus calculations to predict the expected isomerization rates. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478204
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  • 3
    Electronic Resource
    Electronic Resource
    Neutral and cation spectroscopy of fluorene–Arn clusters (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 8239-8251 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fluorene–Arn complexes formed in a pulsed supersonic jet have been studied in their S1 state using two color REMPI spectroscopy with mass resolved detection. The appearance and shifts of the S1 origins relative to the fluorene monomer are measured for cluster sizes up to n=30. The shifts and appearance of these bands are used to identify multiple conformations at low n and have indicated a shift from two sided clustering by Ar at low n to primarily one sided clustering at large n. The ionic ground state of the smaller clusters (n≤6) are studied using mass analyzed threshold ionization (MATI) spectroscopy. The change of the ionization potentials as a function of cluster size has been determined. In the case of the fluorene–Ar4 cluster, the MATI spectrum of two separate cluster conformations was measured, revealing significantly different ionization potentials. Vibrational dynamics has been studied in several smaller clusters (n≤3) by measuring MATI and ZEKE spectra when pumping vibronic transitions in the fluorene chromophore. Significantly enhanced coupling of the chromophore to van der Waals modes is observed in going from n=1 to n=3. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475159
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  • 4
    Electronic Resource
    Electronic Resource
    Electronic spectroscopy and dynamics of the monomer and Arn clusters of 9-phenylfluorene (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 7113-7123 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spectrum of the S1 electronic state of jet-cooled 9-phenylfluorene–Arn, n=0–4, has been measured by two color resonant enhanced multiphoton ionization spectroscopy. The cation ground states of these complexes have also been studied by mass analyzed threshold ionization (MATI) spectroscopy in a 1+1 excitation process with various intermediate states in S1. Ab initio calculations in conjunction with the spectroscopy have determined that the phenyl ring at the 9 position is perpendicular to the plane of the fluorene moiety yielding an overall symmetry of Cs. The Ar complexes for n=1–3 exhibit multiple isomers which are identified in the S1 spectrum and confirmed by MATI spectroscopy. The structure of these isomers is determined by spectral analysis and additivity rules as well as atom–atom calculations using a Lennard-Jones potential. Vibrational dynamics from selected S1 vibronic levels are observed by the appearance of the picosecond or nanosecond time delayed MATI spectra. Vibrational redistribution and dissociation of the clusters are measured with nanosecond and picosecond time resolution. It is found that different isomers of the n=1 cluster show dramatically different rates of redistribution for several vibronic bands. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477395
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  • 5
    Electronic Resource
    Electronic Resource
    Dynamics of vibronically excited fluorene–Arn (n=4, 5) clusters (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9632-9638 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The fluorene–Ar4 cluster has been shown to exhibit two distinct isomers when formed in a molecular beam. Resonance enhanced multiphoton ionization and mass analyzed threshold ionization experiments have been performed to investigate the structural properties, energetics and dynamics of these clusters when excited to vibronic bands in the S1 electronic state, with a specific interest in measuring isomer interconversion. At 208 cm−1 excess energy in the S1 isomer interconversion is not observed in the Ar4 cluster. Dissociation of the Ar5 cluster from the 722 cm−1 band is shown to produce both Ar4 isomers. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476439
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  • 6
    Electronic Resource
    Electronic Resource
    Design and development of a rapid acquisition laser-based fluorometer with simultaneous spectral and temporal resolution (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 3061-3072 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report the design, development, and characterization of a sensitive, time-resolved fluorescence spectrometer capable of measuring fluorescence spectra and transient decays simultaneously, with data acquisition times less than 1 s. The spectrometer, a portable fluorescence lifetime spectrometer (FLS), was designed to be compatible with both laboratory and clinical research studies on biological systems, and was applied to the study of several biological fluorophores in vitro and human tissue in vivo. The instrument consisted of a nitrogen laser pumping a dye laser for excitation from 337.1 nm through the near infrared, a quartz fiber-optic probe for remote light delivery and collection, and amplified detectors for rapid spectral and temporal detection from 350 to 800 nm. The spectral resolution of the FLS was determined to be 3 nm, which is sufficient for accurately detecting the broad spectral bands associated with biological fluorophores. The FLS was able to detect 5×10−7 M fluorescein dye concentrations with spectral signal-to-noise ratios (SNRs) of 29. Time-resolved detection with the FLS had a dynamic range of approximately three decades with a SNR of 200. Using fluorescence lifetime standards, the FLS was determined to be capable of accurately resolving fluorophore lifetimes from hundreds of picoseconds to tens of nanoseconds in duration, with an ultimate temporal resolution of 360 ps. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1379957
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  • 7
    Electronic Resource
    Electronic Resource
    3-Ethylindole electronic spectroscopy: S1 and cation torsional potential surfaces (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 1857-1865 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The tryptophan derivative 3-ethylindole was studied in the first excited electronic state and the cation ground state using resonance enhanced multiphoton ionization (REMPI) and zero electron kinetic energy (ZEKE) spectroscopy. Weakly bound clusters of 3-ethylindole with argon (n=1–3) have also been studied. The monomer spectroscopy revealed that two conformations of the 3-ethylindole exist in the jet cooled sample. Density-functional theory (DFT) calculations have been used to calculate the ground- and ionic-state geometries and energies. The calculations reveal the two conformations to be a planar and a nonplanar orientation of the ethyl substituent relative to the indole plane. The ZEKE spectrum of the nonplanar form has an extensive progression in the vibration associated with ethyl torsion and indicates a significant geometry change in the ethyl chain torsion upon ionization. The ethyl chain torsional potential is mapped out using DFT calculations, and the ion surface is adjusted such that calculated frequencies and Franck–Condon factors reproduce the experimental ZEKE spectra. The conformer interconversion barrier height is calculated in the ground and ion states. This is compared to an experimentally determined barrier height in the ion. The spectroscopy of the argon complexes reveals interesting results with regard to the cooling of the 3-ethylindole conformations. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481989
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