The rotational structure of three-photon resonances of polyatomic molecules

Dixon, Ronald; Bayley, J. M.; Ashfold, Michael N. R.

doi:10.1016/0301-0104(84)80003-8

Cited by 83 publications

(28 citation statements)

References 19 publications

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“…5 illustrates that the dramatic difference in the rovibrational product distributions for the 2 dissociation mechanisms stems from the very different topologies of the B and Ã state surfaces, coupled with the different ways in which they are accessed from the C state origin level. Furthermore, it explains the 2 contrasting body-fixed anisotropies noted from the 1 10 4 0 00 data. The C and Ã states are both 1 B 1 states, weakly coupled by a homogeneous perturbation, and all of the relevant forces act within the molecular plane.…”

Section: Discussionmentioning

confidence: 87%

“…The 1 10 4 0 00 transition has the highest rotational anisotropy (Table S1), with maximum alignment to the electric vector (A 0 ϭ ϩ2) of the molecular c axis (which is Ќ to the H-O-H plane and parallel to the C 4X transition moment). The dominance of the high product rotation dissociation mechanism for the parallel detection axis (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…By determining values of the recoil anisotropy parameter ␤ (ϭ ͗3cos 2 Ϫ 1͘ with defined relative to the electric vector) for several transitions we have been able to determine a much more detailed picture of the dissociation in the molecular frame than is possible when exciting to short-lived states. Earlier resonance-enhanced multiphoton spectroscopy of the C state indicated a rotational dependence to the predissociation mechanism (10)(11)(12), and rotationally excited OH(A) products were observed through their A3X fluorescence (13). There is also evidence suggesting an additional rotationally independent predissociation mechanism.…”

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confidence: 96%

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Nonadiabatic dissociation dynamics in H ₂ O: Competition between rotationally and nonrotationally mediated pathways

Yuan

Cheng

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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The photochemistry of H2O in the VUV region is important in interstellar chemistry. Whereas previous studies of the photodissociation used excitation via unbound states, we have used a tunable VUV photolysis source to excite individual levels of the rotationally structured C state near 124 nm. The ensuing OH product state distributions were recorded by using the H-atom Rydberg tagging technique. Experimental results indicate a dramatic variation in the OH product state distributions and its stereodynamics for different resonant states. Photodissociation of H2O(C ) in rotational states with ka ‫؍‬ 0 occurs exclusively through a newly discovered homogeneous coupling to the Ã state, leading to OH products that are vibrationally hot (up to v ‫؍‬ 13), but rotationally cold. In contrast, for H2O in rotationally excited states with ka > 0, an additional pathway opens through Coriolis-type coupling to the B state surface. This yields extremely rotationally hot and vibrationally cold ground state OH(X) and electronically excited OH(A) products, through 2 different mechanisms. In the case of excitation via the 110 4 000 transition the H atoms for these 2 product channels are ejected in completely different directions. Quantum dynamical models for the C -state photodissociation clearly support this remarkable dynamical picture, providing a uniquely detailed illustration of nonadiabatic dynamics involving at least 4 electronic surfaces.photochemistry ͉ water ͉ photodissociation ͉ stereodynamics ͉ VUV photolysis W ater vapor absorbs light at all wavelengths in the vacuum UV region below 200 nm, resulting in fragmentation leading to the production of H and OH free radicals. The OH radical product of this unimolecular process is particularly important through its role in interstellar chemistry (1, 2). Extensive experimental and theoretical studies have revealed a rich structure of absorption bands in this spectral region, and have uncovered several active dissociative mechanisms. However, in most of these studies the excitation of the H 2 O parent molecule has been through dissociative continua, so that the observed dynamics relate to averages over an ensemble of molecules in a range of quantum states.In contrast, the present study uses a tuneable VUV laser to excite H 2 O through an electronic state that is sufficiently longlived to exhibit resolved rotational structure. This reveals 2 completely different dissociation pathways that produce strikingly different rovibrationally excited OH products. Furthermore, the competition between these 2 channels shows a strong dependence on the excited rotational quantum numbers and on the direction of mutual recoil of the H and OH fragments.These studies have led to an understanding of how the dissociation dynamics are controlled by the topologies of the nuclear potential energy surfaces of this model system. Absorption by H 2 O between Ϸ140 and 200 nm is to the first excited singlet state, labeled Ã and of symmetry 1 B 1 . The photodissociation on this state has been studied at both 19...

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Section: Discussionmentioning

confidence: 87%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 96%

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Nonadiabatic dissociation dynamics in H ₂ O: Competition between rotationally and nonrotationally mediated pathways

Yuan

Cheng

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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“…These include: (i) that the lqb,,-aZ+ transition has an abnormally large coherent three photon transition probability relative to, for example, any 1[I 1E+ transition, (ii) that this 1~ u state has a much U--O bigger cross-section for excitation into the ionization continuum and (iii) that, of all the Rydberg states, the 1~ u state is most resistant to predissociation. The relative magnitudes of three photon vibronic tensors have been considered previously for a number of limiting situations [27]. Two such situations have been investigated more fully for the case of acetylene.…”

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confidence: 99%

A¹Φ_uRydberg state of acetylene revealed by gas phase multiphoton ionization spectroscopy

et al. 1985

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A new Rydberg state of acetylene has been identified as a three photon resonance in the four photon ionization spectra of both C2H 2 and C2D 2 . In both isotopic species the zero point level of this new electronic state is sufficiently long lived to support rotational structure. Spectral analysis, including use of the appropriate three photon rotational linestrength theory, enables characterization of the excited state symmetry as 10 u. Quantum defect considerations, and comparisons with recent ab initio calculations, encourage assignment of this 10 u state in terms of the electronic promotion n 3 3d69 ~-n u .~ Possible reasons for the dominance of this 10u-aY+g transition in the 3 + 1 MPI spectrum of acetylene are considered.

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“…3a and 3b depict the photoelectron spectra obtained for (2 + 1) ionization via the $1(3/2) and ground state and the calculation of rotational linestrengths, The latter have been obtained by inserting the wavefunctions for both the ground and excited states, expressed in a parity-conserving Hund's case (a) basis, and matrix elements derived using a conventional linear molecule Hamiltonian [9], into the appropriate expression for the two-photon transition probability [10]. The comparison of experimental with simulated excitation spectra for several possible excited-state symmetries led to the unambiguous conclusion that the transitions observed in Figs.…”

Section: Resultsmentioning

confidence: 99%

Two-photon resonance enhanced MPI-PES above the lowest ionization threshold. Observation of the [a1Δ]5pπ 2Φ state of the SH (SD) radical

Milan

Lange

Western

et al. 1995

Chemical Physics Letters

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The rotational structure of three-photon resonances of polyatomic molecules

Cited by 83 publications

References 19 publications

Nonadiabatic dissociation dynamics in H ₂ O: Competition between rotationally and nonrotationally mediated pathways

Nonadiabatic dissociation dynamics in H ₂ O: Competition between rotationally and nonrotationally mediated pathways

A¹Φ_uRydberg state of acetylene revealed by gas phase multiphoton ionization spectroscopy

Two-photon resonance enhanced MPI-PES above the lowest ionization threshold. Observation of the [a1Δ]5pπ 2Φ state of the SH (SD) radical

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The rotational structure of three-photon resonances of polyatomic molecules

Cited by 83 publications

References 19 publications

Nonadiabatic dissociation dynamics in H 2 O: Competition between rotationally and nonrotationally mediated pathways

Nonadiabatic dissociation dynamics in H 2 O: Competition between rotationally and nonrotationally mediated pathways

A1ΦuRydberg state of acetylene revealed by gas phase multiphoton ionization spectroscopy

Two-photon resonance enhanced MPI-PES above the lowest ionization threshold. Observation of the [a1Δ]5pπ 2Φ state of the SH (SD) radical

Contact Info

Product

Resources

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Nonadiabatic dissociation dynamics in H ₂ O: Competition between rotationally and nonrotationally mediated pathways

Nonadiabatic dissociation dynamics in H ₂ O: Competition between rotationally and nonrotationally mediated pathways

A¹Φ_uRydberg state of acetylene revealed by gas phase multiphoton ionization spectroscopy