Browsing by Author "Endo, Yasuki"

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Conformational analysis of ethyl-substituted Criegee intermediate by FTMW spectroscopy
(2016-12-14)
Cabezas, Carlos
;
Guillemin, Jean-Claude
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Ethyl-substituted Criegee intermediate, C2H5CHOO, has been generated in the discharged plasma of a 1,1-diiodopropane/O-2 gas mixture and spectroscopically characterized by Fourier transform microwave spectroscopy in a pulsed supersonic jet. The comparison between the experimental rotational constants and those calculated ab initio unambiguously confirms the identification of three conformers, providing the definitive probe for their molecular structures. Some of the observed pure rotational transitions show small splittings corresponding to the A/E components due to the threefold methyl internal rotation, which made it possible to determine the barrier heights of the hindered methyl rotation. The conformational abundances as well as the non observation of a plausible fourth conformer have been rationalized in terms of interconversion processes between conformers and interactions between the terminal oxygen and the protons of the ethyl moiety. Published by AIP Publishing.
Conformational preferences of Criegee intermediates: Isopropyl substituted carbonyl oxide
(2018-08-28)
Cabezas, Carlos
;
Guillemin, Jean-Claude
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Three conformers of the isopropyl-substituted Criegee intermediate, (CH3)(2) CHCHOO, have been observed by Fourier transform microwave spectroscopy. The transient species was produced using a pulsed electric discharge of a gas mixture of 1,1-diiodo-2-methylpropane/O-2 diluted in Ar or Ne. The use of different carrier gases in the supersonic expansion reveals the difference of the collisional relaxation process between anti-conformers. The conformational relaxation pathways have been investigated theoretically and are presented as well. In light of these results, the previous study on the ethyl-substituted Criegee intermediate, where the absence of one of the four possible conformers was associated with collisional relaxation processes, has been re-examined. Here we report the detection of a new conformer of the ethyl-substituted Criegee intermediate observed using Ne as the seeding gas. Published by AIP Publishing.
Criegee intermediates meet rotational spectroscopy
(2020-07-02)
Cabezas, Carlos
;
Nakajima, Masakazu
;
Endo, Yasuki
;
應用化學系
;
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.
Detection of a Criegee Intermediate with an Unsaturated Hydrocarbon Substituent: Fourier-Transform Microwave Spectroscopy of Methyl Vinyl Ketone Oxide
(2020-07-30)
Endo, Yasuki
;
Witek, Henryk A.
;
Chung, Chen-An
;
Lee, Yuan-Pern
;
交大名義發表
Pure rotational transitions of methyl vinyl ketone oxide, or the so called methyl-vinyl Criegee intermediate, were observed by Fourier-transform microwave spectroscopy. Among the four possible conformers of this species, predicted by theory within an energy window of 3 kcal/mol, only the lowest-energy conformer, the syn-trans form, was detected in a discharged jet of a 1,3-diiode-but-2-ene (either in Z- or E-conformation) and O-2 mixture diluted in Ar. Thirty pure rotational transitions with internal rotation splitting of the methyl top were observed. The observed frequencies were analyzed by the XIAM program, yielding an internal rotation barrier of 702.8(28) cm(-1), which reasonably agrees with a theoretical value of 680 cm(-1) determined with CCSD(T)/cc-pVTZ.
Detection of Microwave Transitions between Ortho and Para States in a Free Isolated Molecule
(2017-10-25)
Kanamori, Hideto
;
Dehghani, Zeinab. T.
;
Mizoguchi, Asao
;
Endo, Yasuki
;
應用化學系
Microwave transitions between the ortho and para states of the S2Cl2 molecule in a free isolated condition are observed for the first time. In the theoretical treatment, we derive eigenfunctions of an effective Hamiltonian including the ortho-para interaction to calculate the intensities and frequencies of forbidden ortho-para transitions in the cm-wave region and pick up some promising candidates for the spectroscopic detection. In the experiment, transitions of the S2Cl2 molecule under a supersonic jet condition are observed with a Fourier transform microwave spectrometer. Seven hyperfine resolved rotational transitions including the lowest rotational level are detected as the ortho-para transitions at the predicted frequencies within the experimental errors. The observed intensities are about 10(-3) times the allowed transitions, which are consistent with the predictions based on the intensity-borrowing model. This result suggests that the orthopara conversion of this molecule occurs in a few thousand years through spontaneous emission even in a circumstance where molecular collisions occur rarely like in interstellar space.
Fourier transform microwave spectroscopy of Criegee intermediates: The conformational behaviour of butyraldehyde oxide
(2019-03-14)
Cabezas, Carlos
;
Guillemin, Jean-Claude
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Four conformers of the n-propyl-substituted Criegee intermediate, CH3CH2CH2CHOO, also named n-butyraldehyde oxide, have been observed by Fourier transform microwave spectroscopy. The transient species was produced using a pulsed electric discharge of a gas mixture of 1,1-diiodobutane/O-2 diluted in Ar or Ne. The observation of only syn species is in contrast to the results of other previous studies of alkyl-substituted Criegee intermediates, in particular, those for the structural isomers, isobutyraldehyde oxide ((CH3)(2)CHCHOO), and methyl-ethyl-ketone oxide (C2H5C(CH3)OO), for which syn and anti species have been observed coexisting in the gas phase.
Fourier transform microwave spectroscopy of the SiCl+ ion
(2018-03-01)
Tanaka, Keiichi
;
Harada, Kensuke
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Cabezas, Carlos
;
Endo, Yasuki
;
應用化學系
Fourier transform microwave spectra for the J=1 <- 0 and 2 <- 1 rotational transitions of the SiCl+ ion were observed for two isotopologues (Cl-35 and Cl-37) in the ground and the first excited vibrational states of the ground (1)Sigma(+) electronic state. Thanks to the high resolution of the FTMW spectrometer, hyperfine structures due to the quadrupole moment of the chlorine nucleus and the nuclear spin-rotation interaction were fully resolved. The observed FTMW spectra were combined with previously reported MMW and diode laser spectra in an analysis to determine the mass-independent Dunham coefficients U-k,U-l as well as a mass scaling parameter Delta(Cl)(01) = -0.856(30). The equilibrium bond length of SiCl+ determined is r(e) = 1.9439729(10) angstrom and the nuclear quadrupole coupling constant of (SiCl+)-Cl-35 is eQq(e) = -11.8788(23) MHz. (C) 2017 Elsevier Inc. All rights reserved.
Fourier-transform microwave spectroscopy of a halogen substituted Criegee intermediate ClCHOO
(2016-11-14)
Cabezas, Carlos
;
Guillemin, Jean-Claude
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Pure rotational spectra of the chloro-substituted Criegee intermediate (ClCHOO) were observed by Fourier-transform microwave spectroscopy. Two conformers (syn and anti) of the isolated molecule were identified from the rotational spectra of the parent and Cl-37 and C-13 isotopologues detected in natural abundance. Rotational constants, centrifugal distortion constants, and all components of the nuclear quadrupole coupling tensor were determined for both conformers. Structural features of the molecule have been rationalized with supporting ab initio calculations and the natural bond orbital analysis, which suggest that the conformational preferences are driven by hyperconjugative effects. Published by AIP Publishing.
Fourier-transform microwave spectroscopy of dimethyl-substituted Criegee intermediate (CH3)(2)COO
(2016-12-28)
Nakajima, Masakazu
;
Endo, Yasuki
;
應用化學系
;
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 of the H-2-HCN complex
(2012-12-03)
Ishiguro, Masazumi
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Harada, Kensuke
;
Tanaka, Keiichi
;
Tanaka, Takehiko
;
Sumiyoshi, Yoshihiro
Fourier-transform microwave spectroscopy was applied to observe the J = 1-0 rotational transition of the H-2-HCN complex for both the ortho-and para-H-2 species to obtain improved molecular constants by an analysis combined with the millimeter-wave data. It was confirmed that the para-and ortho-H-2 species have different configurations: namely H-2 is attached to the H end of HCN in the former, while to the N end in the latter. For the ortho-H-2 species, the hyperfine splitting due to the magnetic interaction between the hydrogen nuclei was observed to give the nuclear spin-spin coupling constant d(H) = 54.6(38) kHz. (C) 2012 Elsevier B.V. All rights reserved.
Fourier-transform microwave spectroscopy on weakly bound complexes of CH2OO with Ar, CO, and N-2
(2019-08-14)
Nakajima, Masakazu
;
Endo, Yasuki
;
應用化學系
;
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.
High-resolution vibration-rotational spectra and rotational perturbation of the OO-stretching ((6)) band of CH2OO between 879.5 and 932.0 cm(-1)
(2018-10-28)
Luo, Pei-Ling
;
Endo, Yasuki
;
Lee, Yuan-Pern
;
交大名義發表
;
應用化學系
We report the observation of a rotationally resolved (6) band associated with the OO-stretching mode of the simplest Criegee intermediate, CH2OO, in the range of 879.5-932.0 cm(-1) (11.37-10.73 m) at an optical resolution of 0.0015 cm(-1). The spectra were recorded with a tunable cw external-cavity quantum-cascade laser (EC-QCL) system coupled with a Herriott multipass absorption cell. Over one thousand lines were assigned to determine the rovibrational parameters of the (6) band. Rotational parameters A, B, and C and higher-order parameters (J), (JK), (K), (J), and (K) were determined precisely. Rotational perturbations for K-a = 3, K-a = 6, and K-a 11 on high-J levels were observed. In particular, for K-a = 6, frequency shifts as a function of J showed an avoided crossing; the shifts were analyzed in terms of a Coriolis interaction between modes (6) and (8) of CH2OO. According to the distinct temporal profiles, lines of a hot band near 899.5 cm(-1) were also identified.
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
;
Endo, Yasuki
;
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.
Identification and Self-Reaction Kinetics of Criegee Intermediates syn-CH3CHOO and CH2OO via High-Resolution Infrared Spectra with a Quantum-Cascade Laser
(2018-08-02)
Luo, Pei-Ling
;
Endo, Yasuki
;
Lee, Yuan-Pern
;
交大名義發表
;
應用化學系
The Criegee intermediates, carbonyl oxides produced in ozonolysis of unsaturated hydrocarbons, play important roles in atmospheric chemistry. The two conformers of CH3CHOO exhibit distinct reactivity toward several atmospheric species, but a distinct conformer-specific probe is challenging because ultraviolet and infrared absorption bands of syn- and anti-CH3CHOO overlap at low-resolution. Employing a quantum-cascade laser and a Herriott cell, we recorded the O-O stretching bands of CH2OO and syn-CH3CHOO in region 880-932 cm(-1) at resolution 0.0015 cm(-1). In addition to completely resolved vibration rotational lines of CH2OO extending over 50 cm(-1), some spectral lines associated with hot bands were identified. Spectral lines solely due to syn-CH3CHOO were also identified. Probing these lines, we determined the rate coefficient for the self-reaction of syn-CH3CHOO to be k(self) = (1.6 +/-(0.5)(0.6)) x 10(-10) cm(3) molecule(-1) s(-1), about twice that of CH2OO.
Observation of hydroperoxyethyl formate from the reaction between the methyl Criegee intermediate and formic acid
(2020-01-14)
Cabezas, Carlos
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Rapid reactions of carboxylic acids with Criegee intermediates provide efficient gas phase removal processes and are proposed to trigger the formation of new molecular compounds, which are implicated in the growth of atmospheric aerosols. The new adducts formed in these reactions are known as hydroperoxide esters and are predicted to be condensable, with lower vapor pressures than the reactants. We report here the direct detection of hydroperoxyethyl formate (HOOCH(CH3)OCHO) formed in the gas phase reaction between the methyl substituted Criegee intermediate, CH3CHOO, and formic acid. Two different isomers of this hydroperoxide ester have been observed using the combination of pulsed Fourier-transform microwave spectroscopy with isotopic substitution experiments and high-level quantum chemical calculations. The identification of hydroperoxyethyl formate as the main nascent product of the CH3CHOO and HCOOH reaction differs from previous results that reported the formation of vinyl hydroperoxide as the reaction product of this reaction.
Probing Criegee intermediate reactions with methanol by FTMW spectroscopy
(2020-06-28)
Cabezas, Carlos
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Criegee intermediates (CIs) are carbonyl oxides generated from ozonolysis of unsaturated hydrocarbons in the atmosphere. The relatively long lifetime of CIs makes possible the bimolecular reactions with other atmospheric agents. These reactions can potentially be fast enough to contribute significantly to the tropospheric budgets of those species or to alter the rate of generation of secondary organic aerosols (SOAs). In particular, the new adducts formed in these reactions contribute SOA formation because they have larger molecular weights and lower vapor pressures than the reactants and are more condensable. alpha-alkoxyalkyl hydroperoxides are the nascent products derived from the insertion reactions of CIs with alcohols. In this work we report the direct detection of methoxymethyl hydroperoxide (HOOCH2OCH3, MMHP) and methoxyethyl hydroperoxide (HOOC(CH3)HOCH3, MEHP) as the reaction products between the CIs, CH2OO and CH3CHOO and methanol. High resolution Fourier transform microwave spectroscopy has been used to identify one and two conformers of MMHP and MEHP, respectively. The pre-reactive complex CH2OO-CH3OH was not observed in this experiment, which indicates that CH2OO shows a different reactivity toward methanol than that toward water. Our results for CH3CHOO + CH3OH show that MEHP is produced in similar ratios whensyn- andanti-CH3CHOO react with methanol vapor.
Probing the conformational behavior of the doubly substituted methyl-ethyl Criegee intermediate by FTMW spectroscopy
(2017-05-07)
Cabezas, Carlos
;
Guillemin, Jean-Claude
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Four conformers of the doubly substituted methyl-ethyl Criegee intermediate, C2H5C(CH3) OO, have been observed by Fourier-transform microwave spectroscopy. The transient species was produced using a pulsed electric discharge of a gas mixture of 2,2-diiodobutane/O-2. The conformational preferences differ from those observed previously for related alkyl-substituted Criegee intermediates. The observation of small splittings in the spectra due to the internal rotation of only one methyl group enabled us to determine the barrier heights of the hindered methyl rotation for the four conformers, which have been compared with those reported for other methyl-substituted Criegee intermediates. Published by AIP Publishing.
Probing the methyl torsional barriers of the doubly substituted methyl-ethyl Criegee intermediate by FTMW spectroscopy
(2018-11-01)
Cabezas, Carlos
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Kleiner, Isabelle
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Carvajal, Miguel
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Endo, Yasuki
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應用化學系
In a previous work, Cabezas et al., 2017 [21], we reported the rotational study of the doubly substituted methyl-ethyl Criegee intermediate, C2H5C(CH3)OO, by using Fourier transform microwave spectroscopy. Four different conformers were found showing AIE splittings due to the internal rotation of methyl tops. However for one of the conformers, syn2, some of the observed lines showed additional splitting that could not be assigned. The present work has been aimed to shed light on these transition line splittings of the syn2 conformer which are assigned to additional splittings coming from the two nonequivalent tops. As a consequence, 182 lines have been observed and the analysis of the internal rotation motions of two non-equivalent methyl tops enabled us to determine the barrier heights of the hindered methyl rotation of the two tops. (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.