Browsing by Author "Dyakov, Yuri A."

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Ion Intensity and Thermal Proton Transfer in Ultraviolet Matrix-Assisted Laser Desorption/Ionization
(2014-04-17)
Lu, I-Chung
;
Lee, Chuping
;
Chen, Hui-Yuan
;
Lin, Hou-Yu
;
Hung, Sheng-Wei
The ionization mechanism of ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI) was investigated by measuring the total cation intensity (not including sodiated and potasiated ions) as a function of analyte concentration (arginine, histidine, and glycine) in a matrix of 2,4,6-trihydroxyacetophenone (THAP). The total ion intensity increased up to SS times near the laser fluence threshold as the arginine concentration increased from 0% to 1%. The increases were small for histidine, and a minimal increase occurred for glycine. Time-resolved fluorescence intensity was employed to investigate how analytes affected the energy pooling of the matrix. No detectable energy pooling was observed for pure THAP and THAP/analyte mixtures. The results can be described by using a thermal proton transfer model, which suggested that thermally induced proton transfer is crucial in the primary ion generation in UV-MALDI.
Ionization and Dissociation Processes of Pyrrolidine in Intense Femtosecond Laser Field
(2009-07-09)
Wang, Qiaoqiao
;
Wu, Di
;
Zhang, Dongdong
;
Jin, Mingxing
;
Liu, Fuchun
Ionization and dissociation mechanisms of pyrrolidine in 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. Singly charged parent ion and numerous fragment ions are observed in the mass spectra, which are investigated as a function of laser intensity and polarization. In order to understand the details of the ionization processes of pyrrolidine in intense femtosecond laser field, we quantitatively calculate the rate constants and ion yields by means of generalized Keldysh-Faisal-Reiss theory, and the excitation probabilities of the excited states are also calculated by using Floquet theory. The results suggest that the ionization might occur partially through the excited states of neutral pyrrolidine. Comparing with linearly polarized (LP) laser field, we observe some enhancement of fragmentation with a circularly polarized (CP) laser field above the saturation threshold intensity which might be explained by the active energies of the pyrrolidine molecular ions are different under CP and LP laser irradiated. To interpret the dissociation patterns of the pyrrolidine ions, we have used the Rice-Ramsperger-Kassel-Marcus theory with the potential surfaces obtained from the ab initio quantum chemical calculations.
Ionization/dissociation processes of methyl-substituted derivates of cyclopentanone in intense femtosecond laser field
(2013-10-24)
Wang, Qiaoqiao
;
Dyakov, Yuri A.
;
Wu, Di
;
Zhang, Dongdong
;
Jin, Mingxing
Ionization and dissociation of 2- and 3-methyl cyclopentanones have been investigated in molecular beams by their irradiation with intense 394 and 788 nm laser fields with pulse duration of 90 fs and intensity of 3 x 10(13)-4 x 10(14) W/cm(2). The analysis of the resulting mass spectra allowed us to discern the effects of methyl substitution and its position on the outcome of ionization/dissociation processes induced by the intense femtosecond laser field. Generalized Keldysh-Faisal-Reiss (g-KFR) and ab initio G3(MP2, CCSD)//B3LYP/6-31G*/RRKM theoretical calculations helped to uncover the formation mechanism of major ionic fragments observed in the mass spectra including C5H10+, C4H6O+, C3H3O+, C3H4O+, C3Hx+, and C2Hx+. (C) 2013 Elsevier B.V. All rights reserved.