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  • American Institute of Physics (AIP)  (24)
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  • 1
    Electronic Resource
    Electronic Resource
    Heterodyne-detected time-domain measurement of I2 predissociation and vibrational dynamics in solution (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 5544-5547 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462693
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  • 2
    Electronic Resource
    Electronic Resource
    Fluorescence-detected wave packet interferometry. II. Role of rotations and determination of the susceptibility (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4180-4194 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The recently developed technique of time-resolved spectroscopy with phase-locked optical pulse pairs is further explored with additional experimental data and more detailed comparison to theory. This spectroscopic method is sensitive to the overall phase evolution of an optically prepared nuclear wave packet. The phase locking scheme, demonstrated for the B←X transition of gas phase molecular iodine, is extended through the use of in-quadrature locked pulses and by examination of the dispersed fluorescence signal. The excited state population following the interaction with both pulses is detected as the resultant two-field-dependent fluorescence emission from the B state. The observed signals have periodically recurring features that result from rovibrational wave packet dynamics of the molecule on the excited state electronic potential energy curve. Quantum interference effects cause the magnitude and sign of the periodic features to be strongly modulated. The two-pulse phase-locked interferograms are interpreted with first order time-dependent perturbation theory. Excellent agreement is found between the experimental interferograms and those calculated from literature values of the parameters governing the electronic, vibrational and rotational structure of I2. A relationship between the phase-locked interferograms and the time-dependent linear susceptibility is obtained. The in-phase and in-quadrature phase-locked interferograms together provide a complete record of the optical free induction decay. Thus by combining the in-phase and in-quadrature data, we obtain the contributions to both the absorptive and dispersive linear susceptibilities arising from transitions within the pulse spectrum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462837
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  • 3
    Electronic Resource
    Electronic Resource
    Subpicosecond predissociation dynamics of the methyl radical Rydberg 3 s state (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 270-276 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The subpicosecond dissociation dynamics of the methyl radical 3 s Rydberg state have been examined using rotational resonance Raman spectroscopy. The rovibronic dependence of the excited state predissociation rates and lifetimes are obtained for the B˜ state origin vibrational level of CH3 and CD3. Analysis of the tunneling rates using a cubic potential barrier yields estimates for the height (2200 cm−1) and position of the barrier along the dissociation coordinate (1.38 A(ring)). A comparison of the potential energy surface parameters for the Rydberg 3 s states of methyl radical and ammonia is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460394
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  • 4
    Electronic Resource
    Electronic Resource
    The spontaneous resonance Raman scattering of CH3I in a supersonic jet (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2806-2817 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The resonance Raman scattering of methyl iodide cooled in neat and seeded supersonic jets has been observed. The incident radiation is resonant with the X→B Rydberg transition (∼200 nm). To our knowledge this is the first reported observation of the resonance Raman scattering of jet-cooled species. Depolarization ratio measurements determine the rotational temperature of the molecular beam to be 10 K (4% CH3I/2 atm He). The only observed spectral evidence of (CH3I)n species (n≥2) in the cooled molecular beam is the appearance of the resonance Raman spectra of I2 produced by the photodecomposition of methyl iodide clusters. The nascent I2 is born with an extremely hot (∼1000 K) vibrational distribution. The excitation profile of the I2 vibrational resonance Raman scattering reveals that the absorption band of the clusters are much broader than that of the monomer. Semiempirical calculations (AM1) predict a CH3I dimer with a bent "heat-to-head'' ground-state equilibrium structure which is a favorable orientation for the production of I2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457927
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  • 5
    Electronic Resource
    Electronic Resource
    Rovibrational Raman scattering of CH3I vapor: Resonance with a perpendicularly polarized electronic transition (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4115-4124 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Raman scattering due to resonance with a perpendicularly polarized electronic transition of a symmetric top molecule in the gas phase is described in a sum-over-all-states approach. The derived intensity and depolarization ratio expressions in an irreducible two-photon tensor basis are applied to the analysis of the ν2 (a1 ) and ν6 (e) bands of CH3 I derived from resonance with the predissociated X→B absorption system. A lifetime of 0.5±0.1 ps is determined for the electronic origin and several K-specific rovibronic levels of the v'6 =1 band of the resonant excited state. These results are contrasted with recent dynamical interpretations of the corresponding jet-cooled CH3 I absorption spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455770
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  • 6
    Electronic Resource
    Electronic Resource
    Nonlinear polarization description of phase-locked pulse-pair spectroscopy (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 4704-4713 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The recently demonstrated technique of optically phase-locked pulse-pair (PLPP) excited spontaneous emission is described by a third-order perturbative density matrix approach. A nonlinear polarization description shows how PLPP spectroscopy depends on all the relevant material dephasing time scales. The time and frequency integrated resonance spontaneous emission consists entirely of resonance fluorescence, and is derived exclusively from excited-state population decay terms, i.e., diagonal second-order density-matrix elements. These third-order polarization results are proportional to the previously derived linear polarization expressions found to describe the observed PLPP I2 vapor emission. The nonlinear treatment allows a comparison of this technique to other forms of ultrafast pump–probe spectroscopies such as transient absorption and photon echo techniques. The role of impulsively prepared coherences is clearly described by this analysis. The effect of pulse duration, relative to material dephasing times, is explored for relaxation given by the optical Bloch equations. The most significant differences between a linear and nonlinear polarization treatment occur for pulse durations greater than the optical dephasing time or when excited state population and coherence decays are of the order of rovibrational periods. A fluorescence line narrowing effect, due to short pulse excitation, is predicted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463872
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  • 7
    Electronic Resource
    Electronic Resource
    Mode-specific subpicosecond photodissociation dynamics of the methyl iodide B state (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 288-296 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibronically specific, subrotational period lifetimes of the predissociated B state (201–190 nm) of CH3I and CD3I are determined by spontaneous resonance Raman scattering measurements of depolarization ratios and rotationally resolved Raman excitation profiles (REPs). The lifetime of the electronic origin, methyl rocking (ν6), and methyl umbrella (ν2) band are the same in CH3I (0.5 ps) and CD3I (1.2 ps). However, the predissociation rate decreases by a factor of ∼3 when one quantum of ν3, the methyl–iodine stretch, is excited on the B-state surface. The only vibrational mode which is found to accelerate the B-state predissociation rate is the a1 C–H (C–D) stretch. The lifetime of the ν1 vibronic level decreases by nearly an order of magnitude for CH3I (60 fs) and by a factor of 2 for CD3I (0.6 ps) relative to the corresponding electronic origin level. In addition, K-resolved REP analysis reveals predissociation rates to be K independent. These mode-specific predissociation rates are ascribed to the shape of the multidimensional reaction coordinate in the region of the curve crossing between the bound (B state) and unbound surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461485
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  • 8
    Electronic Resource
    Electronic Resource
    An experimental study of radiation-induced pure dephasing: ArF excited emission of O2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8605-8615 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effects of incoherent incident light on both nonresonant and resonant secondary radiation (RSR) are demonstrated for the spontaneous emission of O2. ArF excimer radiation (FWHH∼120 cm−1) is resonant with several rovibronic features of the v'=4 band of the Schumann–Runge absorption system. Off-resonant contributions to the RSR spectrum are Raman-like (v‘=1) but carry the linewidth of the incident incoherent radiation. Purely resonant emission features are found to be entirely fluorescence-like (v‘≥6). Other RSR vibrational bands of O2 exhibit contributions of both types of emission including interferences between Raman (off-resonant) and fluorescence (resonant) amplitudes. The observed depolarization ratios also reflect these various emission characters. The RSR spectra of O2 excited by incoherent (ArF) driving fields are contrasted with that due to monochromatic excitation. Convolution of the incident spectral density with a rovibronic Kramers–Heisenberg irreducible tensor treatment of resonance Raman scattering cross sections is shown to capture all the observed RSR emission characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459247
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  • 9
    Electronic Resource
    Electronic Resource
    Depolarization ratios of resonance Raman scattering in the gas phase (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4125-4143 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: All three scattering invariants, isotropic, antisymmetric, and anisotropic, contribute to the resonance Raman (RR) activity of randomly oriented gas phase scatterers as shown in a sum-over-all-rovibronic-states approach regardless of the symmetry of the vibrational transition. Thus, in the gas phase, totally symmetric modes may have Raman depolarization ratios (ρ)〉3/4 and nontotally symmetric modes may have ρ≠3/4 for resonance excitation frequencies. Large ρ dispersion effects are predicted when the RR scattering cross section is dominated by the contribution of a single vibronic band. The extent of this purely rotational effect sensitively depends on the excitation frequency and the resonant dephasing rate. These depolarization ratio effects are demonstrated by the resonance Raman scattering of CH3I (B state) and NH3, ND3 (A state) for both a and e vibrational bands as well as for J (NH3) and K (CH3I) resolved rovibrational features.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455771
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  • 10
    Electronic Resource
    Electronic Resource
    Rotational hyper-Raman excitation profiles: Further evidence of J-dependent subpicosecond dynamics of NH3 (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4692-4699 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Resonance hyper-Raman (RHR) excitation profiles of rovibrational transitions of NH3 are observed as the incident blue radiation is tuned through two-photon resonance with the v‘2 =2 and v‘2 =3 bands of the UV X→A Rydberg transition. The excitation frequency dependence of the rotationally resolved HREPs are fit by our previously derived intensity expressions [L. D. Ziegler et al., J. Chem. Phys. 87, 4498 (1987)]. These fits to theory reveal J-dependent photodissociation rates for both vibronic bands on the A state surface that correspond to subpicosecond lifetimes. The rotationally assisted dynamical effects are consistent with the previous results of linear rotational Raman excitation profile studies and with an adiabatic centrifugal mechanism which couples rotational motion with the photodissociative reaction coordinate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455663
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