Browsing by Author "Dyakov, Y. A."

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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.
Photodissociation of 1,3,5-triazine: An ab initio and RRKM study
(2007-09-27)
Dyakov, Y. A.
;
Mebel, A. M.
;
Lin, S. H.
;
Lee, Y. T.
;
Ni, C.-K.
The ab initio/Rice-Ramsperger-Kassel-Marcus (RRKM) approach has been applied to investigate the photodissociation mechanism of 1,3,5-triazine at different wavelengths of the absorbed photon. Reaction pathways leading to various decomposition products have been mapped out at the G3(MP2,CC)//B3LYP level, and then the RRKM and microcanonical variational transition state theories have been applied to compute rate constants for individual reaction steps. Relative product yields (branching ratios) for the dissociation products have been calculated using the steady-state approach. The results show that, after being excited by 275, 248, or 193 nm photons, the triazine molecule isomerizes to an opened-ring structure on the first singlet excited-state potential energy surface (PES), which is followed by relaxation into the ground electronic state via internal conversion. On the contrary, excitation by 285 and 295 nm photons cannot initiate the ring-opening reaction on the excited-state PES, and the molecule relaxes into the energized ring isomer in the ground electronic state. The dissociation reaction starting from the ring isomer is calculated to have branching ratios of various reaction channels significantly different from those for the reaction initiating from the opened-ring structure. The existence of two distinct mechanisms of 1,3,5-triazine photodissociation can explain the inconsistency in the translational energy distributions of HCN moieties at different wavelengths observed experimentally.
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.