Browsing by Author "Chao, S. D."

Now showing 1 - 13 of 13

A master equation approach to the dynamics of zero electron kinetic energy (ZEKE) states and ZEKE spectroscopy
(2011-02-14)
Wang, Yi-Hsieh
;
Mineo, H.
;
Chao, S. D.
;
Selzle, H. L.
;
Neusser, H. J.
We have theoretically studied important dynamic processes involved in zero electron kinetic energy (ZEKE) spectroscopy using the density matrix method with the inverse Born-Oppenheimer approximation basis sets. In ZEKE spectroscopy, the ZEKE Rydberg states are populated by laser excitation (either a one- or two- photon process), which is followed by autoionizations and l-mixing due to a stray field. The discrimination field is then applied to ionize loosely bound electrons in the ZEKE states. This is followed by using the extraction field to extract electrons from the ZEKE levels which have a strength comparable to that of the extraction field. These extracted electrons are measured for the relative intensities of the ion states under investigation. The spectral positions are determined by the applied laser wavelength and modified by the extraction electric field. In this paper, all of these processes are conducted within the context of the density matrix method. The density matrix method can provide not only the dynamics of system's population and coherence (or phase) but also the rate constants of the processes involved in the ZEKE spectroscopy. Numerical examples are given to demonstrate the theoretical treatments. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3547363]
Autoionization rate constants of zero electron kinetic energy Rydberg states
(2012-03-13)
Mineo, H.
;
Wang, Y. H.
;
Chao, S. D.
;
Lin, S. H.
;
應用化學系
We have calculated the vibrational and rotational autoionization rate constants for diatomic molecules H-2, N-2, and HCl in high Rydberg states by employing the density matrix formulation with the inverse Born-Oppenheimer approximation basis set. The purpose is to simulate the main radiationless processes occurring in zero electron kinetic energy (ZEKE) spectroscopy. The quantum numbers and the energy dependences of the calculated autoionization rate constants are represented as the scaling laws via nonlinear regression. These data provide a suitable starting point for quantitative study of the intricate dynamics involved in ZEKE Rydberg states. (C) 2012 Elsevier B. V. All rights reserved.
Experimental and theoretical investigation of high-power laser ionization and dissociation of methane
(2007-09-27)
Sharifi, A.
;
Kong, F.
;
Chin, S. L.
;
Mineo, H.
;
Dyakov, Y.
The main purpose of this paper is to report the high-power laser ionization-dissociation of CH4 at various femtosecond (fs) laser intensities (from 1 x 10 14 W/cm(2) to 2 x 1015 W/cm(2)) with a laser pulse duration of 48 fs. The generalized molecular Keldysh theory has been applied to calculate the ionization yields for CH4+ and CH4++. Outside the influence of the A intense laser, we propose to calculate the mass spectra due to the decomposition of CH4+ and CH4++, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The agreement between the experimental mass spectra and calculated mass spectra seems to be reasonable.
Experimental and theoretical investigations of ionization/dissociation of cyclopentanone molecule in a femtosecond laser field
(2008-11-28)
Wang, Qiaoqiao
;
Wu, Di
;
Jin, Mingxing
;
Liu, Fuchun
;
Hu, Feifei
The ionization/dissociation mechanism of cyclopentanone has been experimentally investigated in molecular beam by irradiating with intense 394 and 788 nm laser fields with pulse duration of 90 fs. The range of laser intensities varied from 3 X 10(13) to 4 X 10(14) W/cm(2). For both wavelengths, the singly charged parent ion is observable while the doubly charged one cannot be found easily, although the fragmentation pattern supports its presence. Meanwhile, the extent of fragmentation at 788 nm is less than that in the 394 nm case. We quantitatively analyze the ionization processes of cyclopentanone in intense femtosecond laser by comparing the calculation results of ionization rate constants obtained from Ammosov-Delone-Krainov, Keldysh, and Keldysh-Faisal-Reiss (KFR) theories based on hydrogenlike atom model. We also compare the experimental and theoretical results; the generalized KFR theory is found to be useful in predicting the ionization yields of singly and doubly charged cyclopentanone ion. To interpret the dissociation patterns of the cyclopentanone ions, we have used the Rice-Ramsperger-Kassel-Marcus theory with the potential surfaces obtained from the ab initio quantum chemical calculations. (c) 2008 American Institute of Physics.
Highly multiphoton molecular excitation by an intense laser pulse
(2008)
Teranishi, Y.
;
Hayashi, M.
;
Kong, F.
;
Chin, S. L.
;
Chao, S. D.
Multiphoton excitation of molecules by an intense laser field is treated. When the first excitation energy is much larger than both the photon energy and the transition energy between excited states, excited states are strongly coupled with each other by the photon, even though coupling with the ground state is weak. In such a case, a kind of collective excitation takes places, in which the excitation probability of every excited state is almost linear as functions of intensity on a log-log plot, and the slope is independent of the final state. By taking methane and formaldehyde as examples we numerically study this process.
Molecular ionization of cyclohexanone in femtosecond laser fields: An application of ADK theory
(2009-08-01)
Wang, Q. Q.
;
Mineo, H.
;
Wu, D.
;
Jin, M. X.
;
Chin, C. H.
The mechanisms of ionization and dissociation of cyclohexanone (C(6)H(10)O) in a 90 fs, 788 nm linearly polarized laser field ranging from 10(13) to 10(14) W/cm(2) by a time-of-flight mass spectrometer (TOF-MS) have been investigated. The ion yields as a function of laser intensity have been measured experimentally. By comparison with the Ammosov-Delone-Krainov (ADK) theory based on a hydrogen-like model, the ionization mechanism of cyclohexanone in this intense femtosecond laser field has been understood. Considering the importance of molecular nuclear motions, we propose that the Franck-Condon (F-C) factor can provide the excess vibrational energy in the molecular ion. This energy is required for the decomposition of the molecular ion which finally results in the observed mass spectrum.
Structure and predissociation of the 3p sigma(u)D (3)Sigma(+)(u) Rydberg state of N(2): First extreme-ultraviolet and new near-infrared observations, with coupled-channels analysis
(2008-11-28)
Wang, Qiaoqiao
;
Wu, Di
;
Jin, Mingxing
;
Liu, Fuchun
;
Hu, Feifei
The 3p sigma(u)D (3)Sigma(+)(u) Rydberg state of N(2) is studied experimentally using two high-resolution spectroscopic techniques. First, the forbidden D (3)Sigma(+)(u)-X (1)Sigma(+)(g) transition is observed for the first time via the (0,0) band of (14)N(2) and the (1,0) band of (15)N(2), using 1 extreme-ultraviolet +1 ultraviolet two-photon-ionization laser spectroscopy. Second, the Rydberg-Rydberg transition D (3)Sigma(+)(u)-E (3)Sigma(+)(g) is studied using near-infrared diode-laser photoabsorption spectroscopy, thus extending the previous measurements of Kanamori [J. Chem. Phys. 95, 80 (1991)], to higher transition energies, and thereby revealing the (2,2) and (3,3) bands. The combined results show that the D(v=0-3) levels exhibit rapidly increasing rotational predissociation as v increases, spanning nearly four orders of magnitude. The D-state level structure and rotational predissociation signature are explained by means of a coupled-channels model which considers the electrostatically coupled (3)Pi(u) Rydberg-valence manifold, together with a pure-precession L-uncoupling rotational interaction between the 3p sigma(u)D (3)Sigma(+)(u) and 3p pi(u)G (3)Pi(u) Rydberg p-complex components.
Structure and predissociation of the 3p sigma(u)D (3)Sigma(+)(u) Rydberg state of N(2): First extreme-ultraviolet and new near-infrared observations, with coupled-channels analysis
(2008-11-28)
Wang, Qiaoqiao
;
Wu, Di
;
Jin, Mingxing
;
Liu, Fuchun
;
Hu, Feifei
The 3p sigma(u)D (3)Sigma(+)(u) Rydberg state of N(2) is studied experimentally using two high-resolution spectroscopic techniques. First, the forbidden D (3)Sigma(+)(u)-X (1)Sigma(+)(g) transition is observed for the first time via the (0,0) band of (14)N(2) and the (1,0) band of (15)N(2), using 1 extreme-ultraviolet +1 ultraviolet two-photon-ionization laser spectroscopy. Second, the Rydberg-Rydberg transition D (3)Sigma(+)(u)-E (3)Sigma(+)(g) is studied using near-infrared diode-laser photoabsorption spectroscopy, thus extending the previous measurements of Kanamori [J. Chem. Phys. 95, 80 (1991)], to higher transition energies, and thereby revealing the (2,2) and (3,3) bands. The combined results show that the D(v=0-3) levels exhibit rapidly increasing rotational predissociation as v increases, spanning nearly four orders of magnitude. The D-state level structure and rotational predissociation signature are explained by means of a coupled-channels model which considers the electrostatically coupled (3)Pi(u) Rydberg-valence manifold, together with a pure-precession L-uncoupling rotational interaction between the 3p sigma(u)D (3)Sigma(+)(u) and 3p pi(u)G (3)Pi(u) Rydberg p-complex components.
Theoretical and Experimental Investigations of Ionization-Dissociation of Polyatomic Molecules
(2009)
Wang, Qiaoqiao
;
Jin, Mingxing
;
Ding, Dajun
;
Mineo, H.
;
Chao, S. D.
The Keldysh theory originally developed for the ionization of Is state of hydrogen atom has been generalized for molecules by introducing the molecular orbital theory and the Born-Oppenheimer approximation. Ionization and dissociation mechanisms of cyclopentanone in the intense 800 nm laser field (10(13) to 10(14) W/cm(2)) have been experimentally investigated by using a method of molecular beam and time-of-flight mass spectrometer (TOF-MS). Singly-charged parent ion and numerous fragment ions are observed in the mass spectra, which are analyzed by using the molecular Keldysh theory.
Theoretical studies of ZEKE spectroscopy and dynamics of high Rydberg states
(2010-02-12)
Wang, Yi-Hsieh
;
Teranishi, Y.
;
Mineo, H.
;
Chao, S. D.
;
Selzle, H. L.
A main purpose of this Letter is to show how to employ the inverse Born-Oppenheimer approximation as a basis set to study zero kinetic energy (ZEKE) spectroscopy and the autoionization dynamics of the ZEKE states. The calculations of channel couplings, quantum defects, intensity borrowing, vibrational and rotational autotionizations will be demonstrated by using a homonuclear diatomic molecule as an example. (C) 2010 Elsevier B. V. All rights reserved.
Ultrafast coherent dynamics of nonadiabatically coupled quasi-degenerate excited states in molecules: Population and vibrational coherence transfers
(2012-01-02)
Mineo, H.
;
Kanno, M.
;
Kono, H.
;
Chao, S. D.
;
Lin, S. H.
Results of a theoretical study of ultrafast coherent dynamics of nonadiabatically coupled quasi-degenerate pi-electronic excited states of molecules were presented. Analytical expressions for temporal behaviors of population and vibrational coherence were derived using a simplified model to clarify the quantum mechanical interferences between the two coherently excited electronic states, which appeared in the nuclear wavepacket simulations [M. Kanno, H. Kono, Y. Fujimura, S. H. Lin, Phys. Rev. Lett 104 (2010) 108302]. The photon-polarization direction of the linearly polarized laser, which controls the populations of the two quasi-degenerate electronic states, determines constructive or destructive interference. Features of the vibrational coherence transfer between the two coupled quasi-electronic states through nonadiabatic couplings are also presented. Information on both the transition frequency and nonadiabatic coupling matrix element between the two states can be obtained by analyzing signals of two kinds of quantum beats before and after transfer through nonadiabatic coupling. (C) 2011 Elsevier B. V. All rights reserved.
Ultrafast electronic motion in hydrogen molecular ions induced by a high power intense laser
(2010-10-20)
Mineo, H.
;
Teranishi, Y.
;
Chao, S. D.
;
Lin, S. H.
;
應用化學系分子科學碩博班
In this Letter we report a method for controlling electronic localization in a molecular ion, on an attosecond time scale, using a high-intensity laser, based on two different excitation mechanisms. One takes place during ionization, and the other takes place sequentially, following ionization. The electronic excited states of the hydrogen molecular ion are created during ionization by taking the configuration interaction mixing of neutral molecules into account. We detect the ultrafast oscillatory electronic motion between two atoms in a hydrogen molecular ion occurring due to the creation of excited states during the course of ionization. (c) 2010 Elsevier B.V. All rights reserved.
Ultrafast electronic motion in hydrogen molecular ions induced by a high power intense laser
(2010-10-20)
Mineo, H.
;
Teranishi, Y.
;
Chao, S. D.
;
Lin, S. H.
;
應用化學系
In this Letter we report a method for controlling electronic localization in a molecular ion, on an attosecond time scale, using a high-intensity laser, based on two different excitation mechanisms. One takes place during ionization, and the other takes place sequentially, following ionization. The electronic excited states of the hydrogen molecular ion are created during ionization by taking the configuration interaction mixing of neutral molecules into account. We detect the ultrafast oscillatory electronic motion between two atoms in a hydrogen molecular ion occurring due to the creation of excited states during the course of ionization. (c) 2010 Elsevier B.V. All rights reserved.