Some computationally based speculations on the photochemistry of ammonia clusters

Cao, H. Z.; Evleth, E. M.; Kassab, E.

doi:10.1063/1.447756

Cited by 40 publications

(13 citation statements)

References 14 publications

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“…Unfortunately, in the case of longer duration laser pulses (picosecond to nanosecond), a molecular ion produced early in the laser pulse is capable of absorbing additional photons that will invariably induce subsequent dissociation. This second mechanism for dissociative ionization is called absorption-ionization-dissociation 36 (AID) or the ladder climbing mechanism. An example is shown in Figure 2b where molecule ABC absorbs one (or more) photon(s) to produce ABC + .…”

Section: Introductionmentioning

confidence: 99%

Photoexcitation, Ionization, and Dissociation of Molecules Using Intense Near-Infrared Radiation of Femtosecond Duration

1999

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The coupling mechanism between an intense (∼10 13 W cm -2 , 780 nm) near-infrared radiation field of duration 50-200 fs with molecules having 5-50 atoms is considered in this article. In general, the interaction of intense radiation fields with molecules can result in both electron emission and subsequent dissociation. For the laser excitation scheme employed here, intact ions are observed in addition to dissociative ionization channels for all classes of molecules investigated to date. An excitation mechanism is considered where the electric field of the laser mediates the coupling between the radiation and the molecule. This field-induced ionization is compared with the more common frequency-mediated coupling mechanism found in multiphoton processes. Measurements of intense-laser photoionization probability are presented for several series of molecules. An outline of our structure-based model is presented to enable calculation of relative tunneling rates and prediction of the laser-molecule coupling mechanism. The relative ion yields for various series of hydrocarbon molecules are found to be in good agreement with that predicted by the structure-based tunnel ionization model. Measurements of photoelectron kinetic energy distributions also suggest that the ionization phenomena proceed to a large degree through a field-mediated excitation process. The photoionization/ dissociation products are measured in an ion spectrometer and are interpreted in terms of a competition between electronic excitation and energy transfer to nuclear degrees of freedom. Evidence for field-induced dissociation is presented.

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Section: Introductionmentioning

confidence: 99%

Photoexcitation, Ionization, and Dissociation of Molecules Using Intense Near-Infrared Radiation of Femtosecond Duration

1999

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“…7 Increasing the intensity of a resonant nanosecond excitation laser can result in fragmentation of cluster systems 8 via the absorption-dissociation-ionization mechanism. 9 Recent in-vestigations of photoionization using femtosecond excitation pulses, however, reveal no increase in fragmentation with increasing pulse intensity over several orders of magnitude. 10,11 The use of ultrafast radiation can also reduce the subsequent absorption of photons by the ion state thus limiting the absorption-ionization-dissociation mechanism.…”

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confidence: 99%

Near-infrared femtosecond photoionization/dissociation of cyclic aromatic hydrocarbons

DeWitt

Levis

1995

The Journal of Chemical Physics

109

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Pulses of 780 nm light of duration 170 fs and power densities up to 3.8ϫ10 13 W cm Ϫ2 are used to study the photoionization/dissociation processes in the series of gas phase, cyclic aromatic hydrocarbons including benzene, naphthalene, phenanthrene, and anthracene. The near-infrared ionization process leads to the production of intact molecular ions for all of the molecules studied. Measurements of the ion intensity as a function of laser fluence revealed the order of the ultrafast ionization process to be 8.0Ϯ0.1 for anthracene, 6.9Ϯ0.1 for phenanthrene, 8.5Ϯ0.1 for naphthalene, and 8.1Ϯ0.1 for benzene. The relative femtosecond photoionization cross section decreased from 1.0 for anthracene to 0.2 for phenanthrene to 0.1 for naphthalene to ϳ0.005 for benzene. The relative order and cross section of the femtosecond ionization processes suggest that a field ionization mechanism is operative.

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“…An alternative mechanism has been proposed on the basis of earlier theoretical calculations. 32,33 In this scheme, shown in the top sequence in Figure 2, a dissociation step occurs between the absorption of the first and second photons. We will refer to this process as an absorption-dissociation-ionization mechanism (ADI).…”

Section: Discussionmentioning

confidence: 99%

Dissociation dynamics and multiphoton ionization mechanism of ammonia clusters

Misaizu¹,

Houston²,

Nishi³

et al. 1989

J. Phys. Chem.

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Two-color, two-photon ionization of ammonia has been used to investigate the ionization and dissociation mechanisms of ammonia clusters. By observing the ion signals in a reflectron time-of-flight mass spectrometer as a function of the delay time between the two laser pulses, it is found that the lifetime of the intermediate to formation of (NH3)2H+ and higher mass cluster ions is at least 500 times longer than that to formation of NH4+ and (NH3)2+. Similar results are found for deuterated ammonia. The intermediate is formed by one-photon excitation in the energy range accessing the A IA2 state of ammonia. This observation confirms that the mechanism of ionization of the dimer in this energy region is two-photon ionization followed by the rapid intracluster proton-transfer reaction (NH3)2+ -NH4+ + NH2 The mechanism for ionization of larger clusters is discussed.

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Some computationally based speculations on the photochemistry of ammonia clusters

Cited by 40 publications

References 14 publications

Photoexcitation, Ionization, and Dissociation of Molecules Using Intense Near-Infrared Radiation of Femtosecond Duration

Photoexcitation, Ionization, and Dissociation of Molecules Using Intense Near-Infrared Radiation of Femtosecond Duration

Near-infrared femtosecond photoionization/dissociation of cyclic aromatic hydrocarbons

Dissociation dynamics and multiphoton ionization mechanism of ammonia clusters

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