ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Two-color resonant four-wave mixing: Analytical expressions for signal intensity (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3090-3102 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present analytical signal expressions for each two-color resonant four-wave mixing (TC-RFWM) scheme that can be used for double-resonance molecular spectroscopy in the limit of weak fields (no saturation). The theoretical approach employs time-independent, diagrammatic perturbation theory and a spherical tensor analysis in an extension of recent treatments of degenerate four-wave mixing [S. Williams, R. N. Zare, and L. A. Rahn, J. Chem. Phys. 101, 1072 (1994)] and TC-RFWM for the specific case of stimulated emission pumping [S. Williams et al., J. Chem. Phys. 102, 8342 (1995)]. Under the assumption that the relaxation of the population, the orientation, and the alignment are the same, simple analytic expressions are derived for commonly used experimental configurations. The TC-RFWM signal is found to be a product of a concentration term, a one-photon molecular term, a line shape function, and a laboratory-frame geometric factor. These expressions are intended to facilitate the practical analysis of TC-RFWM spectra by clarifying, for example, the dependence on beam polarizations and rotational branch combinations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473052
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Spectroscopic studies of the B˜ 2A′′-X˜ 2A′′ system of the jet-cooled vinoxy radical (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 10048-10065 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply several techniques to the study of the B˜ 2A′′-X˜ 2A′′ band system of the jet-cooled vinoxy radical, CH2CHO. Vibronically resolved excitation spectra are obtained using both laser-induced fluorescence (LIF) and a two-color resonant four-wave mixing (TC-RFWM) scheme that provides the nonlinear equivalent of hole-burning spectra. Rotationally resolved LIF spectra recorded at low temperatures (≤3 K) provide rotational constants for 9 B˜-state levels. We also measure the fluorescence lifetimes of 19 B˜-state levels and obtain high-quality dispersed fluorescence (DF) spectra from seven of the most strongly fluorescing levels in the B˜ state. The excitation and DF spectra reveal far more vibrational levels in the two electronic states than have been previously observed. In total, we provide assignments for 54 levels observed in the first 3650 cm−1 of the B˜ state and for 57 levels in the first 3100 cm−1 of the X˜ state. These assignments include the identification of the a′ fundamentals for ν4 through ν9 and all three a′′ overtones, 2ν10 through 2ν12, in both states. The differences between the TC-RFWM and LIF spectra and the measured lifetimes indicate a dramatic increase in the predissociation rate of the B˜ state beginning at 1190 cm−1 above the origin. The predissociation rate is markedly mode-specific and is enhanced by out-of-plane excitation, possibly due to vibronic coupling with either the A˜ 2A′ or C˜ 2A′ electronic states. The congestion and complexity of the DF spectra at high energies provides direct evidence of extensive intramolecular vibrational redistribution on the ground-state potential surface. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474091
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Laser-induced fluorescence spectroscopy of the ketenyl radical (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 665-668 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the first laser-induced fluorescence (LIF) excitation spectrum of the ketenyl radical, HCCO, which is produced by the 193 nm photolysis of ketene in a free jet expansion. A series of vibronic bands in the B˜ 2Π–X˜ 2A′′ system are observed. The LIF band positions and rotational structures are in excellent agreement with those of a recent photofragment yield (PFY) spectrum [D. L. Osborn et al., J. Chem. Phys. (to be published)] from the origin at 33 424 cm−1 to 35 100 cm−1 . At higher energies the LIF spectrum breaks off sharply due to a rapid increase in the rate of predissociation. The lifetime of the vibrationless level of the B˜ state is less than 1 ns; the estimated quantum yield of fluorescence is ∼10−3. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474427
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Laser-induced fluorescence spectroscopy of the B˜ 2Π–X˜ 2A″ band system of HCCO and DCCO (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 6773-6781 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic spectroscopy of the B˜ 2Π–X˜ 2A″ band system of the ketenyl radical, H(D)CCO, is investigated using laser-induced fluorescence (LIF) in a free-jet environment. Vibronically resolved excitation spectra for HCCO are obtained from 33 400 cm−1 to 35 100 cm−1; at higher energies the LIF spectra cutoff due to a rapid increase in the rate of predissociation. The parallel transitions from Ka″=1 in the ground state to the spin-orbit levels, 2Π3/2 and 2Π1/2, of the origin of the B˜ state are completely rotationally resolved for both HCCO and DCCO. Four other parallel transitions originating from Ka″=0 in the ground state and terminating on levels of Σ vibronic symmetry are observed and assigned to the two pairs of Σ states derived from one quantum of excitation in each of the Renner–Teller active modes, the CCO and CCH(D) bend. Rotational analysis provides effective rotational constants and spin-rotation (orbit) couplings for each of these levels. In addition to the Renner–Teller and spin-orbit couplings, there is substantial evidence for additional perturbations among the low-lying bending levels in the B˜ 2Π state of ketenyl. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478581
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Stimulated emission pumping spectroscopy via two-color resonant four-wave mixing (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8342-8358 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a combined theoretical and experimental study of the application of two-color resonant four-wave mixing (RFWM) to stimulated emission pumping (SEP) spectroscopy. The theoretical approach employs time-independent, diagrammatic perturbation theory and a spherical tensor analysis in an extension of a recent treatment of degenerate four-wave mixing [Williams, Zare, and Rahn, J. Chem. Phys. 101, 1072 (1994)]. The resulting signal expression for two-color RFWM separates the molecular properties from purely laboratory-frame factors determined by the polarizations of the input beams and the rotational branch types of the SEP PUMP and DUMP transitions. This expression is valid in the limit of weak fields and for molecules in which the total angular momentum (omitting nuclear spin) is a good quantum number. In addition, we demonstrate that the spectral response for tuning the DUMP laser is a simple Lorentzian in free-jet experiments. We test our theoretical results and demonstrate the applicability of RFWM-SEP to jet-cooled, transient species in experiments on C3 and HCO. Using the well-studied A˜ 1Πu–X˜ 1Σ+g system of C3, we illustrate and compare the two possible schemes for RFWM-SEP. These are defined as ω1=ω2 (PUMP) and ω3=ω4 (DUMP) or ω1=ω4 (PUMP) and ω2=ω3 (DUMP), where ω1, ω2, and ω3 are the input frequencies and ω4 is the signal frequency.Using the B˜ 2A'–X˜ 2A' system of HCO, we obtain RFWM-SEP spectra that probe ground-state vibrational resonances lying above the low threshold for dissociation to H+CO. Varying the polarization of the input beams or PUMP rotational branch produce dramatic effects in the relative intensities of rotational lines in the RFWM-SEP spectra of HCO; these effects are well-described by our theoretical analysis. Finally, RFWM-SEP spectra of HCO resonances that are homogeneously broadened by dissociation are consistent with the theoretically predicted Lorentzian line shape; the full widths for these levels are in good agreement with those determined via unsaturated fluorescence depletion SEP. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468826
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    SiC2: A molecular pinwheel (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 4110-4126 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the results of a combined experimental and theoretical study of the large-amplitude motion in SiC2 in which the C2 fragment undergoes hindered internal rotation. Stimulated emission pumping (SEP) is used to obtain rovibrational term energies for levels with up to 14 quanta of excitation in the large-amplitude vibration. We analyze the SEP data, as well as other available experimental data, using a semirigid bender model that allows for complete internal rotation within a triatomic molecule. From the least-squares fitting of this model to the data, we determine the potential energy along the minimum energy path of the large-amplitude vibration, the harmonic energies of the small-amplitude vibrations, and the variations of these energies and of the molecular geometry with the large-amplitude coordinate. The fitting is aided by results obtained from ab initio calculations we perform on the triangular and linear configurations of the molecule. The current data set is consistent with a large-amplitude potential energy function in which the energy difference between the triangular and linear configurations is 1883 cm−1. The statistical error on this energy difference is 22 cm−1, but we estimate the physical uncertainty to be about 200 cm−1. This result is in excellent agreement with the energy difference of 1819 cm−1 we obtain in our best ab initio calculations. The semirigid bender fitting and our best ab initio calculations are also both consistent with a potential energy function having no local minimum at linearity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466348
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Laser-induced gratings in free jets. III. Saturation-induced anharmonic gratings (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 856-862 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply two-color laser-induced grating spectroscopy (LIGS) to obtain excitation spectra of the S1(A˜ 1B1)–S0(X˜ 1A1) system of jet-cooled azulene. The ground-state depletion grating created by excitation with crossed beams is probed via either the S2(B˜ 1A1)–S0(X˜ 1A1) or S4(D˜ 1A1)–S0(X˜ 1A1) transitions. First-order LIGS spectra of the S1–S0 origin band at several grating-laser intensities reveal saturation-induced line broadening and significant saturation dips at line center. We develop a simple model, based on the anharmonic grating created in the saturated regime, and use it to fit the first-order data. From these fits we determine a saturation parameter and the linewidth of the S1–S0 origin absorption band, which is homogeneously broadened due to rapid internal conversion (τ∼1 ps) in the S1 state. We also observe LIGS spectra of the azulene origin taken at the second Bragg order of the induced grating; the observed second-order lineshapes are also fit with the anharmonic-grating model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466568
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Experimental and theoretical characterization of the S1–S0 transition of benzo[a]pyrene (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 7323-7335 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We use fluorescence excitation and two-color resonance-enhanced multiphoton ionization (REMPI) spectroscopy to characterize the S1–S0 transition of benzo[a]pyrene, B[a]P. In addition, two-color REMPI with a tunable ionization laser provides an improved measurement of the molecular ionization potential, 7.103±0.004 eV. Ab initio calculations are performed to determine the vibrational frequencies for the 90 vibrational modes in the S1 and S0 electronic states. Our results indicate that the single-excitation configuration interaction (CIS) level of theory provides an excellent representation of excited-state frequencies for this large molecule. Virtually all of the vibronic bands between ∼380 nm and 397 nm, as well as numerous bands between 373 nm and 380 nm, are assigned with the aid of the calculated vibrational frequencies. In total, 27 of the 61 a′ symmetry vibrational modes and 5 of the 29 a″ vibrational modes in the S1 state have now been assigned. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472591
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Direct measurement of rotational energy transfer rate constants for H35Cl (v=1) (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 5229-5237 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate the rotational energy transfer of H35Cl (v=1) in collisions with thermal HCl at 298 K. Rotationally state-selective excitation of v=1 over J=1–6 is achieved by stimulated Raman pumping, and the rotational relaxation from the initially pumped level is monitored via 2+1 resonantly enhanced multiphoton ionization (REMPI) through the E 1Σ+–X 1Σ+0–1 band. The ions are detected in a time-of-flight mass spectrometer in order to ensure that only relaxation of H35Cl is observed. We present empirical correction factors for determining relative rotational populations from the REMPI spectral line intensities and extract the rate constants for rotational energy transfer from the time-dependent populations using numerical techniques. The excellent sensitivity of the REMPI technique makes it possible to monitor the relaxation on very short collisional time scales (〈0.1 hard sphere collision) and thereby enables us to determine the rate constants for both single quantum and multiquanta rotational transitions directly, without the use of a simplifying model for the matrix of rate constants. The measured rate constants illustrate the importance of multiquanta transitions for HCl; such transitions account for ∼30% of the total population loss from a given rotational level. We compare our rate constants to those obtained in previous measurements on HCl (v=1) and HF (v=2). We find that the rate constants are not adequately described by models based solely on the rotational energy defect of the vibrationally excited molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453691
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    UV laser excited fluorescence spectroscopy of the jet-cooled copper dimer (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 6560-6566 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: UV laser excited fluorescence spectra of the jet-cooled copper dimer are reported. Cu2 is produced via laser vaporization of the metal inside the throat of a pulsed, supersonic nozzle. Strong fluorescence is observed upon excitation of 63Cu2 in the range 287–324 nm, corresponding to several v‘=0 bands of the II–X transition recently found in excitation using resonant two-photon ionization [Smalley et al., J. Chem. Phys. 78, 2866 (1983)]. The II–X emission spectra are characterized by extremely long progressions in the ground state vibration, enabling us to measure G(v) and ΔGv+1/2 values over the range v=0–72. This data has been fit to yield improved vibrational constants for 63Cu2 X 1Σ+g@B: ωe =266.43±0.59 cm−1, ωexe =1.035±0.030 cm−1, ωeye =+(1.70±0.58)×10−3 cm−1, and ωeze =−(1.78±0.37)×10−5 cm−1. The G(v) data has also been fit to a near-dissociation expansion which incorporates the correct limiting behavior of G(v), determined by the asymptotic inverse power contribution to the potential. This fit gives an improved dissociation energy for the dimer, and the vibrational index at dissociation: De =16 760±200 cm−1 and vD =128±5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450708
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...