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  • 1
    Electronic Resource
    Electronic Resource
    Influence of methyl group deuteration on the rate of intramolecular vibrational energy relaxation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 1116-1122 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The high resolution spectra of the fundamental and first overtone of the acetylenic C–H stretch in tert.-butylacetylene-d9 and (trimethylsilyl)acetylene-d9 have been measured using optothermal detection of a collimated molecular beam. IVR lifetimes determined from the homogeneously broadened lineshapes are compared to those of their undeuterated analogues. It is found that for both molecules, at both levels of excitation, deuterating the methyl rotors results in an increased rate of IVR. The results indicate that the previously suggested methyl rotor effect, as an enhancer for IVR, plays a secondary role to increasing the number of low order resonances to which the C–H stretch can couple. Although the torsional modes are important for the molecules to exhibit statistical case IVR and contribute to the filled-in homogeneous lineshapes, the rate of energy relaxation seems to be dominated by the number of low order resonances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464336
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  • 2
    Electronic Resource
    Electronic Resource
    The rate of intramolecular vibrational energy relaxation of the fundamental C–H stretch in (CF3)3C–C≡C–H (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 1748-1749 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The high resolution spectrum of the fundamental C–H stretch in (CF3)3C–C≡C–H has been measured using optothermal detection of a collimated molecular beam. Only the Q branch was resolvable and was fit to a Lorentzian with a full width at half maximum of 2.76 GHz, corresponding to an IVR lifetime of 60 ps. The decrease in lifetime in comparison to (CH3)3C–C≡C–H is thought to be due to strong mixing between the C–F stretches and bends and the backbone C–C stretches and bends.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464290
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  • 3
    Electronic Resource
    Electronic Resource
    Molecules excited to regions of high state density are not deflected by an inhomogeneous electric field (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 2477-2480 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Conclusive experimental evidence is presented that molecules excited to a single ro-vibrational eigenstate in a high density-of-states region are not deflected by an inhomogeneous electric field. The onset of nondeflection behavior occurs in the same density of states region as has been found for the onset of intramolecular vibrational energy redistribution IVR (about 10 vibrational states/cm−1). By using large polyatomic molecules, where the hydride stretch fundamentals occur in this range of state density, the nondeflection behavior can be studied. However, the results are generally applicable to the dynamics of smaller molecules at higher levels of excitation. Thus, the observed nondeflection in our experiments is expected to be a general phenomenon associated with highly vibrationally excited molecules. In addition, it is shown how the nondeflection characteristics of these systems can be exploited experimentally to obtain spectra with increased sensitivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464178
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  • 4
    Electronic Resource
    Electronic Resource
    Sub-Doppler, infrared laser spectroscopy of the propyne 2ν1 band: Evidence of z-axis Coriolis dominated intramolecular state mixing in the acetylenic CH stretch overtone (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 2596-2611 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The eigenstate-resolved 2ν1 (acetylenic CH stretch) absorption spectrum of propane has been observed for J'=0–11 and K=0–3 in a skimmed supersonic molecular beam using optothermal detection. Radiation near 1.5 μm was generated by a color center laser allowing spectra to be obtained with a full-width at half-maximum resolution of 6×10−4 cm−1 (18 MHz). Three distinct characteristics are observed for the perturbations suffered by the optically active (bright) acetylenic CH stretch vibrational state due to vibrational coupling to the nonoptically active (dark) vibrational bath states. (1) The K=0 states are observed to be unperturbed. (2) Approximately 2/3 of the observed K=1–3 transitions are split into 0.02–0.25 cm−1 wide multiplets of two to five lines. These splittings are due to intramolecular coupling of 2ν1 to the near resonant bath states with an average matrix element of 〈V2〉1/2=0.002 cm−1 that appears to grow approximately linearly with K. (3) The K subband origins are observed to be displaced from the positions predicted for a parallel band, symmetric top spectrum.The first two features suggest that the coupling of the bright state to the bath states is dominated by parallel (z-axis) Coriolis coupling. The third suggests a nonresonant coupling (Coriolis or anharmonic) to a perturber, not directly observed in the spectrum, that itself tunes rapidly with K; the latter being the signature of diagonal z-axis Coriolis interactions affecting the perturber. A natural interpretation of these facts is that the coupling between the bright state and the dark states is mediated by a doorway state that is anharmonically coupled to the bright state and z-axis Coriolis coupled to the dark states. Z-axis Coriolis coupling of the doorway state to the bright state can be ruled out since the ν1 normal mode cannot couple to any of the other normal modes by a parallel Coriolis interaction. Based on the range of measured matrix elements and the distribution of the number of perturbations observed we find that the bath levels that couple to 2ν1 do not exhibit Gaussian orthogonal ensemble type statistics but instead show statistics consistent with a Poisson spectrum, suggesting regular, not chaotic, classical dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466456
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  • 5
    Electronic Resource
    Electronic Resource
    Reinvestigation of the acetylenic C–H stretching fundamental of propyne via high resolution, optothermal infrared spectroscopy: Nonresonant perturbations to ν1 (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 2588-2595 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the high resolution spectrum of the ν1 fundamental of propyne near 3335 cm−1 obtained using a very warm free jet expansion in our optothermal detection spectrometer. By using a high concentration sample expanded at low backing pressures we have been able to observe transitions for K values up to K=6. The additional data available allow us to reinvestigate this vibrational band. We find an unusual perturbation pattern in this band where the individual subbands (rovibrational transitions for a single K value) appear to be completely unperturbed at the level of precision of our data (7.5 MHz), but the subband origin orderings are perturbed through nonresonant interactions. Attempts to account for the subband ordering using a two-state anharmonic interaction are unsuccessful indicating that the perturbations are of multistate origin. This type of nonresonant perturbation to the subband origins of symmetric top molecules should be a common feature of symmetric tops with large A rotational constants. As a result of this investigation we conclude that the previously reported value of αA, determined from a very cold expansion where only K=0 and K=1 were observed, is not a measure of the true (unperturbed) value of this constant. This conclusion is also supported by force field calculations presented here that use an empirical harmonic force field augmented by diagonal anharmonicities for the hydride stretches. These calculations, which reproduce measured values of αA and αB for lower energy bands quite successfully, also show that the previous determination of αA is too large and must be dominated by perturbation contributions. We have also measured the weak Fermi resonant band ν3+2ν09 which acquires its intensity through interaction with ν1. Again we find an anomalous subband ordering like that observed in ν1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466455
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  • 6
    Electronic Resource
    Electronic Resource
    The molecular Stark effect in regions of high state density: Overall simplicity and underlying complexity in the response to a static electric field (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 6210-6220 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the high-resolution (11 MHz) infrared measurement of the molecular Stark effect for the R(0) transition of the acetylenic C–H stretch in 2-propyn-1-ol. The field-free spectrum is fragmented into three eigenstate components due to the effects of intramolecular vibrational energy redistribution (IVR). As the field strength increases from 0 to 25 kV/cm, the number of eigenstates increases linearly. The center-of-gravity of the fragmented R(0) transition follows the simple, second-order Stark shift (Δν∝E2) expected for the bright state. However, when viewed at the eigenstate level, the mechanism of the Stark shift is rather complex. At lower field strengths, the eigenstates shift in energy, as occurs for Stark effects in lower state density regimes. As the number of coupled states increases, energy shifting of the eigenvalues is quenched. To preserve the second-order Stark shift of the center-of-gravity, the intensity "rolls over'' the largely rigid eigenvalue structure. For molecules in regions of high state density, the reduced energy shifting of the eigenvalues as the electric field is increased means that lack of deflection by inhomogeneous electric fields is not necessarily a consequence of the molecule being nonpolar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467084
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  • 7
    Electronic Resource
    Electronic Resource
    DECODING THE DYNAMICAL INFORMATION EMBEDDED IN HIGHLY MIXED QUANTUM STATES (2000)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physical Chemistry 51 (2000), S. 323-353 
    Details
    ISSN: 0066-426X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The standard description of the vibrational and rotational motion of polyatomic molecules, as expressed by the distortable rotor/harmonic oscillator approximation, provides an adequate description of the molecular quantum states only in regions of low total state density. When the total state density is large, exceeding 100 states/cm-1, the vibrational dynamics are "dissipative" and the fundamental process of intramolecular vibrational energy redistribution is operative. The presence of intramolecular vibrational energy redistribution leads to molecular quantum states of a qualitatively different nature. With respect to a normal-mode vibrational basis, these quantum states are "highly mixed" in their vibrational character and represent nuclear motion that is a combination of all the normal-mode motions. This review describes frequency domain spectroscopy techniques designed to probe the vibrational, rotational, and structural composition of these eigenstates. Recent work that investigates spectroscopy between highly mixed states is also reviewed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.physchem.51.1.323
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  • 8
    Electronic Resource
    Electronic Resource
    The rotational spectrum of a highly vibrationally mixed quantum state. I. Intramolecular vibrational energy redistribution (IVR) exchange narrowing of the rotational spectrum (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 4396-4406 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The description of the rotational spectrum of a single, highly vibrationally mixed molecular eigenstate is given using two formulations. The model studied is a set of anharmonically coupled normal-mode rovibrational states. In the first approach, the rotational problem is cast into the form of the single bright-state model of IVR. This eigenstate-level formulation reveals the fragmentation of the rotational spectrum as the magnitude of the anharmonic coupling is increased. It is also seen that the center frequencies of all of the molecular eigenstate rotational spectra approach the same value, determined by the ensemble average rotational constant, as the IVR rate is increased. Furthermore, this formulation provides a generalization to rotational spectroscopy. When there is extensive state mixing, the center frequency of the pure rotational spectrum of a single molecular eigenstate is determined by the expectation value of the rotational constant, and the width of the spectrum is determined by the quantum mechanical fluctuation of the rotational constant in the molecular eigenstate. The lineshape properties of the spectrum are addressed using the motional (exchange) narrowing formalism for the ensemble spectrum. This formulation provides a quantitative description of the narrowing of the rotational spectrum by an IVR exchange mechanism. Finally, the convergence of the line shape profile of the eigenstate rotational spectrum to the line shape of the ensemble spectrum is investigated using a statistical model Hamiltonian. Convergence is observed when the number of overlapping states, defined as Wrms*ρ, reaches 1. These results show that an experimental measurement of the rotational spectrum of single molecular eigenstates can provide important average properties of the rotational constant distribution, dipole moment distribution, and the IVR rate at a well-defined total energy. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477043
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  • 9
    Electronic Resource
    Electronic Resource
    Structurally mixed molecular eigenstates of 2-fluoroethanol resulting from conformational isomerization (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 8189-8192 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a newly developed method of molecular-beam, infrared-microwave double-resonance spectroscopy, we are able to measure the rotational spectrum of a single molecular eigenstate of the molecular Hamiltonian near 3000 cm−1 of energy above the ground rovibrational state. This energy lies above the barrier to conformation isomerization in many molecules. In the –CH2F asymmetric C–H stretch of the Gg conformer of 2-fluoroethanol, near 2983 cm−1, we demonstrate the contribution of vibrational states localized around the Tt conformer structural minimum to the individual molecular eigenstates. The measurement demonstrates the ability of isolated molecules to use vibrational excitation to achieve geometrical rearrangement. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475119
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  • 10
    Electronic Resource
    Electronic Resource
    Dressed states of molecules and microwave–infrared double-resonance spectroscopic techniques employing an electric quadrupole focusing field (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 10430-10439 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-sensitivity, microwave–infrared double-resonance measurements can be made in molecular-beam spectrometers employing a single state-focusing device. The key feature of the double-resonance technique is the achievement of large signal modulations of infrared signals using microwave transitions, even in cases where the infrared transition cannot be saturated. A series of measurements is presented that shows that the technique is based on the transition moment and state-focusing properties of dressed molecular states in the presence of a strong microwave field. Using a state-focusing device, the spectroscopic measurements are doubly sensitive to the composition of the dressed states. The technique can be extended to other types of spectroscopy, such as electronic spectroscopy and the spectroscopy of weakly bound complexes. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474207
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