Intramolecular quantum chaos in doped helium nanodroplets

Polyakova, Elena; Stolyarov, Daniil; Zhang, X.; Kresin, Vladimir Z.; Wittig, C.

doi:10.1016/s0009-2614(03)00714-0

Cited by 6 publications

(10 citation statements)

References 29 publications

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“…Highly vibronically excited NO 2 molecules have recently been studied in helium droplets. [209] The results show a variety of rather broad (7 cm À1 ) bands, which all have similar shifts from the gas-phase values, which is consistent with quantum chaotic behavior in these highly excited states of NO 2 .…”

Section: Vibrational Line Shifts and Broadeningsupporting

confidence: 68%

Superfluid Helium Droplets: A Uniquely Cold Nanomatrix for Molecules and Molecular Complexes

2004

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Herein, recent experiments on the spectroscopy and chemical reactions of molecules and complexes embedded in helium droplets are reviewed. In the droplets, a high spectroscopic resolution, which is comparable to the gas phase is achieved, while an isothermal low-temperature environment is maintained by evaporative cooling at T =0.37 K (4He droplets) or 0.15 K (3He droplets), lower than possible in most solid matrices. Thus the helium-droplet technique combines the benefits of both the gas phase and the classical matrix-isolation techniques. Most important, the superfluid helium facilitates binary encounters, and absorbs the released binding energy upon recombination. Thus the droplet can be viewed as an isothermal nanoscopic reactor, which isolates single molecules, clusters, or even a single reactive encounter at ultralow temperatures.

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Section: Vibrational Line Shifts and Broadeningsupporting

confidence: 68%

Superfluid Helium Droplets: A Uniquely Cold Nanomatrix for Molecules and Molecular Complexes

2004

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“…Trotz einiger orientierender Theorien56, 67 und indirekter Hinweise67 sind die Details dieses Phänomens nicht vollständig verstanden. Vibronisch hochangeregte NO 2 ‐Moleküle in Heliumtröpfchen wurden kürzlich untersucht 209. Die Spektren zeigen eine Mannigfaltigkeit relativ breiter Banden (7 cm −1 ), die alle um ähnliche Beträge zum Gasphasenwert verschoben sind.…”

Section: Ir‐spektrenunclassified

Suprafluide Heliumtröpfchen: außergewöhnlich kalte Nanomatrices für Moleküle und molekulare Komplexe

Toennies

Vilesov

2004

Angewandte Chemie

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Dieser Aufsatz gibt einen Überblick über neuere Experimente zur Spektroskopie und zu chemischen Reaktionen von Molekülen und Komplexen in Heliumtröpfchen. Im Inneren solcher Matrices wird eine ähnlich hohe spektroskopische Auflösung wie in der Gasphase erzielt, und durch Verdampfungskühlung lässt sich eine isotherme Tieftemperaturumgebung von T=0.37 K (4He‐Tröpfchen) oder 0.15 K (3He‐Tröpfchen) aufrechterhalten – kälter als in den meisten Festkörpermatrices möglich ist. Die Heliumtröpfchentechnik kombiniert somit die Vorteile von Gasphasen‐ und klassischen Matrixisolationstechniken. Ein wichtiger Punkt ist, dass die suprafluide Heliumumgebung binäre Stöße erleichtert und die bei der Rekombination freigesetzte Bindungsenergie absorbiert. Die Tröpfchen lassen sich folglich als isotherme nanoskopische Reaktoren betrachten, in denen Einzelmoleküle, Cluster oder sogar einzelne reaktive Stöße bei ultratiefen Temperaturen isoliert werden können.

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“…These studies were carried out in the energy range 17 700-18 300 cm -1 , where it is known that strong nonadiabatic interaction via conical intersection of the X ˜and A ˜adiabats yields manifolds of A 1 and B 2 vibronic symmetries, each of which can be said to be quantum chaotic. 7,8 Though this spectrum was reported earlier, 6 as it is central to the interpretation of the results presented below, it is given here as Figure 1.…”

Section: Introductionmentioning

confidence: 87%

“…Moreover, vigorous and complex intramolecular vibrational dynamics and their associated dopant−host interactions do not perceive of the host as being merely a quiescent fluid. Rather, in this case, the helium responds as an ensemble of particles, akin to a dense gas, and average line widths of ∼7 cm -1 fwhm have been recorded in absorption spectra of NO 2 embedded in He n . In the quantum liquid, these line widths are homogeneous, so they correspond to subpicosecond deactivation times, which is hardly a small effect.…”

Section: Introductionmentioning

confidence: 99%

“…The NO 2 molecule is an especially attractive candidate for such a study because it places at our disposal a wealth of knowledge about its gas-phase photochemistry, as well as its relaxation in He n in the regime of vibronic chaos. 6 In addition, it provides access to the largest possible gas-phase reaction rate coefficients that are consistent with a unimolecular decomposition mechanism, i.e., k uni values as high as ∼5 × 10 12 s -1 . 13 With larger rate coefficients, it is unreasonable to assume that intramolecular vibrational redistribution (IVR) proceeds much more rapidly than reactionsan assumption that is a basic tenet of the theory of unimolecular decomposition.…”

Section: Introductionmentioning

confidence: 99%

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Photoexcitation of NO₂ in He_n Droplets above the Gas-Phase Dissociation Threshold

2004

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The guest−host dynamics of NO2 embedded in He n droplets have been examined by recording depletion spectra of mass spectrometer signals at m/z values of 8 (He2 +), 30 (NO+), and 46 (NO2 +) throughout the wavelength range 340−402 nm. At energies above the Ã/X̃ conical intersection, gas-phase NO2 is known to exhibit quantum chaos, and it is also known that deactivation of embedded NO2 by the helium host is efficient in this regime. Above the gas-phase dissociation threshold (D 0) it is shown that there is no net unimolecular decomposition all the way up to D 0 + 4300 cm-1. At the upper end of this range, gas-phase NO2 decomposes with rate coefficients whose values are ∼5 × 1012 s - , which is expected to be larger than the deactivation rates in liquid helium. The deactivation rate in the quantum-chaotic region 17 700−18 300 cm-1 was found previously to be ∼1.4 × 1012 s - 1, and it is expected that this will increase at yet higher energies, but not exceed 5 × 1012 s - 1. To within the experimental uncertainty, it is found that reaction products do not leave the droplets. This is attributed to efficient relaxation and (at the highest energies examined) recombination within the droplets. On the basis of these results, it is concluded that small polyatomics embedded in He n droplets that have 〈n〉 values of ∼104 or larger will not undergo net unimolecular reaction if the gas-phase pathway is barrierless, with two possible exceptions: (i) if one or both of the products has a positive chemical potential and (ii) if the scattering cross section of the product(s) with helium is small.

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Intramolecular quantum chaos in doped helium nanodroplets

Cited by 6 publications

References 29 publications

Superfluid Helium Droplets: A Uniquely Cold Nanomatrix for Molecules and Molecular Complexes

Superfluid Helium Droplets: A Uniquely Cold Nanomatrix for Molecules and Molecular Complexes

Suprafluide Heliumtröpfchen: außergewöhnlich kalte Nanomatrices für Moleküle und molekulare Komplexe

Photoexcitation of NO₂ in He_n Droplets above the Gas-Phase Dissociation Threshold

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Intramolecular quantum chaos in doped helium nanodroplets

Cited by 6 publications

References 29 publications

Superfluid Helium Droplets: A Uniquely Cold Nanomatrix for Molecules and Molecular Complexes

Superfluid Helium Droplets: A Uniquely Cold Nanomatrix for Molecules and Molecular Complexes

Suprafluide Heliumtröpfchen: außergewöhnlich kalte Nanomatrices für Moleküle und molekulare Komplexe

Photoexcitation of NO2 in Hen Droplets above the Gas-Phase Dissociation Threshold

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Photoexcitation of NO₂ in He_n Droplets above the Gas-Phase Dissociation Threshold