Creation of Population Inversions in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Λ</mml:mi></mml:math>Doublets of OH by the Photodissociation of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>O at 157 nm: A Possible Mechanism for the Astronomical Maser

Andresen, Peter L.; Ondrey, Gerald; Titze, B.

doi:10.1103/physrevlett.50.486

Cited by 54 publications

(15 citation statements)

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“…This structure indicates the predissociative nature of the process. [6][7][8], which would have been easily discernible just below the observed thresholds for (AK =0) transitions, support further the conclusion that -at least near the thresholds -the contribution of the J~ZB 1 state to the predissociation yield is weak compared to that of the ~ZB 2 state. 5).…”

Section: Discussionmentioning

confidence: 57%

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Near threshold channel selective photodissociation of NO2

Robra

Zacharias

Welge

1990

Z Phys D - Atoms, Molecules and Clusters

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The dynamics of the photodissociation of NO z into NO(X2//e,,, v" =0, J") + O(3PO.l.Z) is investigated near the thermodynamic threshold. Cooling the internal degrees of freedom by a supersonic beam expansion provides a nearly complete quantum state selection prior to the predissociation. Measurements of the wavelength dependent dissociation yield into specific product quantum states are reported. At certain wavelengths A" doublet resolved rotational population distributions of the fragments are obtained. Up to an excess energy of Eoxc = 121 cm-t about 42% of this energy is partitioned into the rotation of the NO molecules, and correspondingly 58% into the translational degree of freedom. The role of electronic and total parity is discussed.

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Section: Discussionmentioning

confidence: 57%

“…This technique has been applied, e.g., to the direct photodissociation of H20 via the .41A 1 state [6], the dissociation of NCNO via the predissociative $ ~A" state [7], and, in preliminary reports from our group, to the photofragmentation of NOz [8]. Then, only a few (1-3) rotational states possess a significant population.…”

Section: Introductionmentioning

confidence: 99%

Near threshold channel selective photodissociation of NO2

Robra

Zacharias

Welge

1990

Z Phys D - Atoms, Molecules and Clusters

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“…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 193 nm 3 and 157 nm (4,5) and found to result in a very low internal excitation of the OH(X 2 ⌸) radical product. This was attributed to dissociation on a single repulsive surface.…”

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confidence: 99%

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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“…Photodissociation of H 2 O on this state has been studied at both 193 nm ͑Ref. 2͒ and 157 nm, [3][4][5] and was found to be a fast and direct dissociation process on a repulsive surface, with low internal excitation of the OH͑X 2 ⌸͒ product.…”

Section: Introductionmentioning

confidence: 99%

Two-photon photodissociation dynamics of H2O via the D̃ electronic state

Yuan

Cheng

et al. 2009

The Journal of Chemical Physics

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Photodissociation dynamics of H(2)O via the D state by two-photon absorption have been investigated using the H-atom Rydberg tagging time-of-flight technique. The action spectrum of the D<--X transition band has been measured. The predissociation lifetime of the D state is determined to be about 13.5 fs. The quantum state-resolved OH product translational energy distributions and angular distributions have also been measured. By carefully simulating these distributions, quantum state distributions of the OH product as well as the state-resolved angular anisotropy parameters were determined. The most important pathway of the H(2)O dissociation via the D state leads to the highly rotationally excited OH(X,v=0) products. Vibrationally excited OH(X) products (up to v=10) and electronically excited OH(A,v=0,1,2) have also been observed. The OH(A)/OH(X) branching ratios are determined to be 17.9% at 244.540 nm (2omega(1)=81,761.4 cm(-1)) and 19.9% at 244.392 nm (2omega(2)=81,811 cm(-1)), which are considerably smaller than the value predicted by the theory. These discrepancies are attributed to the nonadiabatic coupling effect between the B and D surfaces at the bent geometry.

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Creation of Population Inversions in theΛDoublets of OH by the Photodissociation ofH2O at 157 nm: A Possible Mechanism for the Astronomical Maser

Cited by 54 publications

References 9 publications

Near threshold channel selective photodissociation of NO2

Near threshold channel selective photodissociation of NO2

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

Two-photon photodissociation dynamics of H2O via the D̃ electronic state

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Creation of Population Inversions in theΛDoublets of OH by the Photodissociation ofH2O at 157 nm: A Possible Mechanism for the Astronomical Maser

Cited by 54 publications

References 9 publications

Near threshold channel selective photodissociation of NO2

Near threshold channel selective photodissociation of NO2

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

Two-photon photodissociation dynamics of H2O via the D̃ electronic state

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