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  • 1
    Electronic Resource
    Electronic Resource
    The rotational spectrum and structure of chlorine peroxide (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6588-6597 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The products of the ClO self-reaction have been studied in a flowing chemical reactor using submillimeter wave spectroscopy. The complete spectrum between 415 to 435 GHz has been measured as well as selected transitions in the range 285 to 415 GHz. The major products have been identified as the ClO dimer (Cl2O2) and chlorine dioxide (OClO). The observed rotational b-type spectra of the most abundant isotopic species35 ClOO35Cl and 37ClOO35Cl have been analyzed. The observed nuclear spin statistics for the main species, the relative abundance of the lesser species, and the structure determination demonstrate unambigiously that the ClO dimer must possess identical chlorine atoms in a peroxide structure. The rotational constants as well as a complete set of quartic centrifugal distortion constants have been determined. Structural parameters for the vibronic ground state have been calculated: rOO=142.59(21) pm, rClO=170.44(4) pm, (angle)ClOO=110.07(1)° and dihedral angle=81.03(1)°. Rotational transitions in the first excited torsional state have been measured and analyzed for the isotopic species 35,35 and 35,37. An effective molecular structure for the first torsional excited state has been calculated. A torsional frequency has been derived from relative intensity measurements and the cis and the trans barrier heights estimated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457377
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  • 2
    Electronic Resource
    Electronic Resource
    High resolution zero kinetic energy photoelectron spectroscopy of benzene and determination of the ionization potential (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 4737-4744 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the direct high-resolution determination of the ionization potential of benzene and the observation of rotational structure in the vibronic ground state of the benzene ion. We employ a new technique of two-color high-resolution zero kinetic energy photoelectron spectroscopy (ZEKE-PES) via selection of an intermediate resonant (neutral) state. The ZEKE-PES method allows for the investigation of rotationally resolved photoionization dynamics and the direct high-precision determination of ionization potentials, the precision being derived directly from the laser wavelength calibration. For benzene we determine an IP of 74 555.0±0.4 cm−1. We compare this method to ionization potential measurements from ion yield measurements under various conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452694
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  • 3
    Electronic Resource
    Electronic Resource
    Quenching of C2H emission produced by vacuum ultraviolet photolysis of acetylene (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3495-3501 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Excited C2 H* is produced by vacuum ultraviolet photolysis of acetylene using a frequency tripled laser. Time-dependent emission is measured from 400–940 nm. The use of a coherent photolysis source produces an excitation spectrum in which the rotational band contour is resolved. The absorption spectrum of C2 H2 taken in the same apparatus closely resembles the excitation spectrum indicating a homogeneous predissociation. Time-dependent quenching of the C2 H* emission by Xe, Kr, Ar, He, N2, H2, D2, and C2 H2 is measured. The rapid quenching rates and lack of strong dependence on atomic weight suggest a spin-allowed process is involved in this channel of C2 H2 photolysis. Quench rates are compared with several theoretical models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454920
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  • 4
    Electronic Resource
    Electronic Resource
    Pure dephasing of a vibrational adbond (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 7307-7314 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical study of the vibrational relaxation of the adbond between a physisorbed molecule and a crystalline substrate is presented. The bond between the admolecule and the substrate is described as a one-dimensional Morse oscillator. Using standard perturbation theory, expressions for the relaxation of the vibrational adbond due to its interaction with the substrate lattice vibrations are derived. Both energy relaxation and pure dephasing are considered. A numerical evaluation of the resulting expressions for the relaxation constants is given for a Debye spectrum for the phonons and for a surface phonon spectrum. The relative importance of pure dephasing and energy relaxation in determining the absorption linewidth is derived as a function of the fundamental frequency of the active mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453324
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  • 5
    Electronic Resource
    Electronic Resource
    Layer growth mechanism and dipole–dipole interactions of CH3Cl on Pd(100): An infrared and thermal desorption study (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8300-8305 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fourier transform infrared spectroscopy (FTIRS) and temperature programmed desorption (TPD) have been used to study the layer growth mechanism of CH3Cl on a Pd(100) surface at 85 K. Methyl chloride adsorbs and desorbs in molecular form without decomposition. Three different adsorbed states are readily distinguishable by both methods. The chemisorbed state (first layer) saturates at aitch-theta =0.5 coverage, with the characteristic C–H vibrations of 1011, 1330, 1426, 2927 cm−1. The desorption spectrum for this state suggests a coverage-dependent activation energy between 54.5 and 42 kJ/mol. Nearly the same amount of CH3Cl is bonded in the physisorbed state (second layer) with characteristic C–H vibrations at 1013, 1338, 1428, and 2925 cm−1. The activation energy of the desorption in this case is 40–35 kJ/mol. The condensation phase appears only after the completion of the first two layers and exhibits characteristic C–H vibrations at 1023, 1338/1346, 1444, and 2955 cm−1. In a model calculation {developed by Albano [J. Chem. Phys. 86, 1044 (1986)]} it is shown, that the intermolecular dipole–dipole interaction may explain correctly the coverage- dependent activation energy for desorption of methyl chloride.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459312
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  • 6
    Electronic Resource
    Electronic Resource
    On the Born and Markov approximations: Phonon relaxation and coherent excitation of adsorbed molecules (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 5504-5511 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The phonon relaxation of the vibrational adbond of an adsorbed molecule and a phonon-damped adbond irradiated by a laser are studied. In the first half of the paper, approximations are made within the Zwanzig projection operator formalism in order to arrive at a master equation for the reduced density operator of a small subsystem (the adbond) in contact with a reservoir (the phonons). The conditions of validity for the Born and Markov approximations are derived. It is shown that the master equation is only valid for times t(very-much-greater-than)τc, where τc is the characteristic time of the reservoir. These results are then applied to the phonon relaxation of the vibrational adbond of physisorbed molecules. It is shown that for CO adsorbed on Ni or Cu (a strongly bound physisorbed system) the Born and Markov approximations are not justified. For the weakly bound system Ar on W, numerical results show that these approximations can be made. Finally, an adbond interacting with both laser radiation and lattice vibrations is considered. This system can be regarded as a subsystem (the adbond) in contact with two reservoirs, where the conditions for validity of the Markov approximation is then seen to be more severe than when each reservoir is considered independently. For the phonons, these conditions can never be matched. However, for an initial state given by an adbond in equilibrium with the lattice vibrations, the conditions for validity of the approximations prove to be the same as for the phonons and the laser considered independently.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453634
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  • 7
    Electronic Resource
    Electronic Resource
    Time-resolved two-dimensional vibrational spectroscopy of a short α-helix in water (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 7737-7743 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nonlinear two-dimensional (2D) vibrational spectroscopy has been used to investigate the amide I band of an alanine-based 21-residue α-helical peptide in aqueous solution. Whereas the linear absorption spectrum consists of a single, broad amide I band, the 2D vibrational spectrum clearly reveals that this band is composed of two amide I transitions, which are assigned to the A and E1 modes. The A–E1 frequency splitting is found to be approximately 10 cm−1. We find that the amide I band is inhomogeneously broadened due to conformational disorder of the helix. The 2D line shapes can be well described using distributions of the dihedral angles (φ,ψ) around their average values with a width of 20°, confirming previous molecular-dynamics studies. Time-resolved 2D measurements show that the conformation fluctuates on a time scale of picoseconds. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1407842
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  • 8
    Electronic Resource
    Electronic Resource
    Measurement of the V–T energy transfer rates of highly excited 2A1 NO2 (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8040-8046 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Production of electronic ground state NO2 (2A1) from 248 nm photolysis of HNO3 was detected by laser induced fluorescence (LIF). A growth in the LIF signal was observed following the photolysis and has been interpreted as the relaxation of NO2 through the higher vibrational levels of the X(2A1) state; an energy region where the probe laser photodissociates the NO2 instead of inducing fluorescence. The rate coefficients for NO2 relaxation through these high vibrational levels were determined by fits of time resolved LIF signal to a stepladder kinetic model. The results of the kinetic analysis suggest that the observed relaxation begins at the 2B2 threshold near 9500 cm−1 and extends downward through approximately 5 vibrational levels of the ground electronic surface. The derived quenching rate coefficients (in units of 10−12 cm3 molecule−1 s−1) are 0.51±0.05, 1.0±0.1, 1.4±0.2, 2.6±0.6, and 8.7±1.1 for Ar, He, N2, O2, and CO2 collision partners, respectively. The discrepancies between these coefficients and previous literature values are rationalized in terms of a dependence of the vibrational relaxation rate on total internal energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466797
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  • 9
    Electronic Resource
    Electronic Resource
    The OBrO C(2A2)←X(2B1) absorption spectrum (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2300-2307 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The highly structured visible absorption spectrum of the bromine dioxide radical, OBrO, has been observed in the 15 500–26 000 cm−1 region. The spectrum is dominated by a long progression in the Br–O symmetric stretching motion (ν1′) and a series of short progressions built on the bending mode (ν2′); there are no features associated with the excitation of the antisymmetric stretching mode (ν3′). The spectrum also contains numerous transitions originating from the (0,1,0) and (1,0,0) vibrational levels of the electronic ground state, X(2B1). A simultaneous fit to all of the observed vibronic features yielded the frequencies ν1″=799.4 cm−1, ν2″=317.5 cm−1, ω1′=641.5 cm−1, ω2′=210.7 cm−1, and a band origin T0=15 863 cm−1. Franck–Condon simulations combined with ab initio calculations of the four lowest OBrO doublet electronic states identify the spectrum as arising from the C(2A2)←X(2B1) electronic transition. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474606
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  • 10
    Electronic Resource
    Electronic Resource
    Pressure dependence and metastable state formation in the photolysis of dichlorine monoxide (Cl2O) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2857-2868 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation of dichlorine monoxide (Cl2O) was studied using broadband flash photolysis to investigate the influence of variations in the photolysis wavelength domain, bath gas pressure and bath gas identity on the yield and temporal dependence of the ClO product. ClO yields were independent of bath gas pressure when the photolysis spectral band extended to 200 nm (quartz cutoff) but for photolysis restricted to wavelengths longer than about 250 nm, ClO yields decreased with increasing bath gas pressure and there was a pressure-dependent delay in the formation of ClO. Under these conditions, a weak, highly structured absorption spectrum was observed in the range 16 600–26 000 cm−1 with a lifetime on the order of 500 ms. A portion of the spectrum could be analyzed (22 000–26 000 cm−1) which showed progressions having differences of 283, 443, and 505 cm−1. Ab initio calculations were performed to evaluate vertical excitation energies and oscillator strengths from the lowest-energy singlet (X 1A1) or triplet (1 3B1) states to various excited states. The calculations indicated that the 2 3A2←1 3B1 transition has an unusually large oscillator strength. The transition energy, 3.05 eV, is consistent with the observed metastable spectrum. The observed pressure dependence of ClO formation could be modeled using a mechanism which assumed that Cl2O excitation at wavelengths longer than about 300 nm leads to rapid intersystem crossing to two metastable states in the triplet manifold. These states undergo competitive dissociation to ClO+Cl and collisional relaxation to the ground state. The dynamics of Cl2O may serve as a model for other molecules of importance in the earth's lower stratosphere such as ClONO2 where filtering of the solar spectrum by ozone restricts photolysis to the weak tail of the absorption continuum. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471109
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