Angle-resolved Beutler-Fano profile and dynamics for the predissociation of ${\mathbf{H}}_{\mathbf{2}}$

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Angle-resolved Beutler-Fano profile and dynamics for the predissociation of $H_{2}$

Qingnan Meng, Jie Wang, and Yuxiang Mo

Phys. Rev. A 93, 050501(R) – Published 6 May 2016

Abstract

The asymmetric photoabsorption line profile (Beutler-Fano profile) arising from two interacting channels has applications in atomic, molecular, and condensed matter physics. In this work, the angle-resolved and fully-rotationally-resolved Beutler-Fano profiles for the predissociation of $H_{2}, H_{2} + h v \to H (1 s) + H (2 s) / H (2 p)$ , have been measured. It is found that the Beutler-Fano profiles display different shapes for the fragments H( $2 s, 2 p$ ) recoiling at the parallel and perpendicular directions relative to the polarization direction of the dissociation laser. Tuning the excitation photon energy from the resonance center to the lower energies within the Beutler-Fano profile, the branching ratios H( $2 s$ )/[H( $2 s$ )+H( $2 p$ )] decrease, and the fragment angular distributions change in a trend indicating the presence of more components of direct dissociation channels in comparison with the predissociation channel.

Received 21 January 2016

DOI:https://doi.org/10.1103/PhysRevA.93.050501

Physics Subject Headings (PhySH)

Photodissociation

Molecules

Photoexcitation

Atomic, Molecular & Optical

Authors & Affiliations

Qingnan Meng, Jie Wang, and Yuxiang Mo^*

Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084, China

^*ymo@mail.tsinghua.edu.cn

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Vol. 93, Iss. 5 — May 2016

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Figure 1
The H fragment yield spectrum for the predissociation of $H_{2}$ for the $R$ (0) and $R$ (1) transitions in $3 p π D^{1} Π_{u}^{+} (υ = 4) \leftarrow X^{1} Σ_{g}^{+} (υ^{''} = 0)$ . The dark (thin) lines are the experimental data, and the red (thick) line is the nonlinear least-squares fitting to determine the parameters of the line profiles. The arrows indicate the energy positions at which the velocity map images of the fragments have been measured. The asterisk indicates at which a time-of-flight spectrum of the H Rydberg atoms has been measured (see Fig. 2).
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Figure 2
Time-of-flight spectrum of the H Rydberg atoms at an excitation energy of $121 054 c m^{- 1}$ at which the two transitions $R$ (0) and $R$ (1) in $3 p π D^{1} Π_{u}^{+} (υ = 4) \leftarrow X^{1} Σ_{g}^{+} (υ^{''} = 0)$ appear simultaneously. The excitation energy is marked by the arrow with an asterisk symbol in Fig. 1. The angles between the polarization direction of the XUV laser and the recoil fragment velocity vector are (a) 4° and (b) 84° at the center-of-mass coordinate.
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Figure 3
Angle- and rotationally resolved Beutler-Fano profiles for the $R$ (1) and $R$ (0) transitions in $3 p π D^{1} Π_{u}^{+} (υ = 4) \leftarrow X^{1} Σ_{g}^{+} (υ^{''} = 0)$ . Panels (a) and (c) correspond to $R$ (1), and panels (b) and (d) to $R$ (0). The angles between the fragment recoil direction and the polarization direction of the XUV laser are 4° and 84° in the center-of-mass coordinate for panels (a), (b) and (c), (d), respectively. The dark (thin) lines are from the experimental data measured with a gas mixture (10% Ar+90% $H_{2}$ ). For the $R$ (1) transition the data in the energy range $121 007 - 121 015 c m^{- 1}$ (between the two dotted lines) are from the experimental data measured with a pure $H_{2}$ beam in order to avoid an accidental (1+1) resonance-enhanced ionization of Ar. The red (thick) lines are from the nonlinear least-squares fittings with the parameters listed in Table 1.
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Figure 4
(a) Velocity map images at the peak of the $R$ (0) transition. (b) Velocity map images at four different excitation frequencies within the $R$ (1) profile. The polarization of the XUV laser is along the up and down direction. The colors are so indexed that the signal intensities increase from the centers of the images to the bright rings. (c) The angular distributions of the photofragments extracted from the corresponding velocity map images for the $R$ (0) transition and (d) for the $R$ (1) transition. The anisotropy parameters β determined from the nonlinear least-squares fitting are listed in Table 2.
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Figure 5
The fragment H( $2 s, 2 p$ ) signal intensities as a function of the delay time between the pump and the probe laser pulses under field-free conditions. The solid squares and the dotted lines are the experimental data and the simulation to determine the branching ratio H( $2 s$ )/[H( $2 s$ )+H( $2 p$ )] for the $R$ (0) transition, respectively. The open symbols and the continuous lines are the experimental data and the simulations for the $R$ (1) transitions, respectively. The corresponding excitation photon energies and the determined branching ratios can be found in Table 2.
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Physical Review A

covering atomic, molecular, and optical physics and quantum information

Angle-resolved Beutler-Fano profile and dynamics for the predissociation of $H_{2}$

Qingnan Meng, Jie Wang, and Yuxiang Mo

Phys. Rev. A 93, 050501(R) – Published 6 May 2016

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Physical Review A

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Angle-resolved Beutler-Fano profile and dynamics for the predissociation of H2

Qingnan Meng, Jie Wang, and Yuxiang Mo

Phys. Rev. A 93, 050501(R) – Published 6 May 2016

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Angle-resolved Beutler-Fano profile and dynamics for the predissociation of $H_{2}$