Browsing by Author "Nakajima, Masakazu"

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Criegee intermediates meet rotational spectroscopy
(2020-07-02)
Cabezas, Carlos
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Nakajima, Masakazu
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Endo, Yasuki
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應用化學系
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Department of Applied Chemistry
Carbonyl oxides, R1R2COO, alternatively known as Criegee intermediates (CIs), are short-lived molecules produced from ozonolysis of alkenes. These ozonolysis reactions yield highly excited CIs, and most of them promptly decay with emission of the OH radical and other products. Some of the nascent CIs are stabilised by collisional relaxation with surrounding molecules, and react with atmospheric trace constituents, such as SO(2)and gaseous organic compounds, converting them to more highly oxygenated molecules relevant to formation of aerosols. Hence, reactions of CIs are of central interest for atmospheric chemists. Physico-chemical properties of CIs are strongly related to their geometrical and electronic structures, which are often discussed based on spectroscopic information. Especially, very high resolution rotational spectroscopy provides critical information about molecular structures and intramolecular dynamics, and also enables us to probe individual isomers, conformers, and isotopologues, with complete selectivity. This article reviews the rotational investigations carried out on several CIs, their bimolecular complexes and primary reaction products, focusing on their molecular structure, conformational behaviour and reactivity.
Dynamics of the reactions of O(D-1) with CD3OH and CH3OD studied with time-resolved Fourier-transform IR spectroscopy
(2012-10-28)
Huang, Chong-Kai
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Xu, Zhen-Feng
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Nakajima, Masakazu
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Nguyen, Hue M. T.
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Lin, M. C.
We investigated the reactivity of O(D-1) towards two types of hydrogen atoms in CH3OH. The reaction was initiated on irradiation of a flowing mixture of O-3 and CD3OH or CH3OD at 248 nm. Relative vibration-rotational populations of OH and OD (1 <= nu <= 4) states were determined from their infrared emission recorded with a step-scan time-resolved Fourier-transform spectrometer. In O(D-1) + CD3OH, the rotational distribution of OD is nearly Boltzmann, whereas that of OH is bimodal; the product ratio [OH]/[OD] is 1.56 +/- 0.36. In O(D-1) + CH3OD, the rotational distribution of OH is nearly Boltzmann, whereas that of OD is bimodal; the product ratio [OH]/[OD] is 0.59 +/- 0.14. Quantum-chemical calculations of the potential energy and microcanonical rate coefficients of various channels indicate that the abstraction channels are unimportant and O(D-1) inserts into the C-H and O-H bonds of CH3OH to form HOCH2OH and CH3OOH, respectively. The observed three channels of OH are consistent with those produced via decomposition of the newly formed OH or the original OH moiety in HOCH2OH or decomposition of CH3OOH. The former decomposition channel of HOCH2OH produces vibrationally more excited OH because of incomplete intramolecular vibrational relaxation, and decomposition of CH3COOH produces OH with greater rotational excitation, likely due to a large torque angle during dissociation. The predicted [OH]/[OD] ratios are 1.31 and 0.61 for O(D-1) + CD3OH and CH3OD, respectively, at collision energy of 26 kJ mol(-1), in satisfactory agreement with the experimental results. These predicted product ratios vary weakly with collision energy. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4759619]
Fourier-transform microwave spectroscopy of dimethyl-substituted Criegee intermediate (CH3)(2)COO
(2016-12-28)
Nakajima, Masakazu
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Endo, Yasuki
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應用化學系
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Department of Applied Chemistry
Pure rotational transitions of the dimethyl-substituted Criegee intermediate (dimethyl carbonyl oxide, acetone oxide), (CH3)(2)COO, were observed in the discharge plasma of a C(CH3)(2)I-2/O-2 gas mixture by Fourier-transform microwave spectroscopy. The observed spectra show small splittings due to the internal rotations of the two methyl groups. Precise rotational constants of the molecule and the barrier heights of the methyl internal rotations were experimentally determined. Published by AIP Publishing.
Fourier-transform microwave spectroscopy on weakly bound complexes of CH2OO with Ar, CO, and N-2
(2019-08-14)
Nakajima, Masakazu
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Endo, Yasuki
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應用化學系
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Department of Applied Chemistry
Pure rotational transitions of weakly bound complexes of the simplest Criegee intermediate CH2OO with Ar, CO, and N-2 are observed by Fourier-transform microwave (FTMW) and FTMW-MW double-resonance spectroscopy. Many of the observed lines show doublet peaks associated with the tunneling splitting between the two equivalent configurations of the complexes. The intermolecular distances of the complexes are derived from the precise rotational constants determined in this study. The separations between two components of the doublet peaks observed for c-type transitions of CH2OO-Ar are satisfactorily demonstrated by a one-dimensional hindered rotor model for the internal rotation of the CH2OO monomer. Published under license by AIP Publishing.
Hyperfine analysis of the microwave spectrum of the vinylthio radical, CH2CHS
(2018-11-01)
Nakajima, Masakazu
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Tokumasu, Takanobu
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Sumiyoshi, Yoshihiro
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Endo, Yasuki
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應用化學系
Measurement of pure rotational transitions for the vinylthio radical, CH2CHS, previously observed by Fourier-transform microwave spectroscopy (Nakajima et al., 2007), are extended to a number of fine and hyperfine component lines split by the unpaired electron spin and the three non-equivalent protons. All the measured transition frequencies have been analyzed by a Hamiltonian for doublet asymmetric top molecules with hyperfine interaction terms for three nuclear spins, yielding precise molecular constants of CH2CHS in the ground state. Discussions on the electronic structure of CH2CHS are given based on the determined molecular constants. (C) 2018 Elsevier Inc. All rights reserved.
Pure rotational spectrum of cis-OSOO
(2019-06-16)
Nakajima, Masakazu
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Endo, Yasuki
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應用化學系
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Department of Applied Chemistry
Pure rotational transitions of cis-OSOO are identified in a discharge plasma of a SO2 and O-2 gaseous mixture by Fourier-transform microwave (FTMW) and FTMW-MW double-resonance spectroscopy. Both a- and b-type transitions are observed for this molecule, and the rotational and centrifugal distortion constants are precisely determined from the observed line positions. The inertial defect calculated from the determined rotational constants indicates that the cis-OSOO molecule has a planar equilibrium geometry in the ground vibronic state.
Pure rotational spectrum of HCI
(2019-08-01)
Nakajima, Masakazu
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Endo, Yasuki
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應用化學系
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Department of Applied Chemistry
The 1(01)-0(00) and 2(02)-1(01) rotational transitions of a monohalomethylene, HCI, are observed in a discharge plasma of diiodomethane by Fourier-transform microwave (FTMW) and FTMW-microwave double-resonance spectroscopy. The effective rotational constant (B + C)/2, the centrifugal distortion constant Delta(J), and the quadrupole coupling constant of the iodine nucleus are determined from the observed line frequencies. The nuclear spin-rotation coupling constant C-bb is required to be included into the set of fitting parameters for a satisfactory analysis of the observed line frequencies. (C) 2019 Elsevier Inc. All rights reserved.