Browsing by Author "Cabezas, Carlos"

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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.
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
;
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.
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
;
Kleiner, Isabelle
;
Carvajal, Miguel
;
Endo, Yasuki
;
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.
Spectroscopic Characterization of the Reaction Products between the Criegee Intermediate CH2OO and HCl
(2017-07-19)
Cabezas, Carlos
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Pulsed Fourier-transform microwave experiments have been performed to probe the products resulting from the reaction between HCl and the simplest Criegee intermediate, CH2OO, where the reaction is considered to be important in atmospheric chemistry. The experimentally determined rotational parameters interpreted with the help of quantum chemical calculations support the identification of chloro-methyl hydroperoxide molecule as the primary product of this reaction.
The Criegee intermediate-formic acid reaction explored by rotational spectroscopy
(2019-09-07)
Cabezas, Carlos
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
The atmospheric reaction of the simplest Criegee intermediate, CH2OO, with formic acid has been investigated in the gas phase by pulsed Fourier-transform microwave spectroscopy. The dominant nascent product from this reaction was identified as hydroperoxymethyl formate (HOOCH2OCHO), for which two different conformations, formed through independent insertion mechanisms, were observed in the discharged plasma of a CH2I2/O-2/formic acid gas mixture. The conformational identifications are supported by the observation of C-13 species in natural abundance together with the chemically mono substituted deuterium isotopologues. These isotopic observations further suggest that hydroperoxymethyl formate slightly decomposes, producing formic anhydride (OHCOCHO) in a dehydration reaction.
The reaction between the methyl Criegee intermediate and hydrogen chloride: an FTMW spectroscopic study
(2018-09-21)
Cabezas, Carlos
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
Experiments using pulsed Fourier-transform microwave spectroscopy have been performed to probe the reaction between the methyl substituted Criegee intermediate, CH3CHOO, and hydrogen chloride. Two conformers of the product derived from the insertion of HCl within CH3CHOO, chloroethyl hydroperoxide, formed in the discharged plasma of a CH3CHI2/O-2/HCl gas mixture, were identified through their experimentally determined rotational and quadrupole coupling constants. The relative abundance of the detected species indicates that the reaction of the anti-CH3CHOO conformer is faster than that of the syn-CH3CHOO conformer. The results presented in this work constitute the first experimental information about the reaction between CH3CHOO and HCl.
The reactivity of the Criegee intermediate CH3CHOO with water probed by FTMW spectroscopy
(2018-01-07)
Cabezas, Carlos
;
Endo, Yasuki
;
應用化學系
;
Department of Applied Chemistry
The reaction of Criegee intermediates with water is one of the dominant removal mechanisms for these species in the atmosphere. The reactivity of alkyl substituted Criegee intermediates has been shown to be affected by the nature and location of the substituents. CH3CHOO, acetaldehyde oxide, can be considered as a prototypical Criegee intermediate with a single alkyl substituent to examine the conformer specific reactivity for Criegee intermediates. Pulsed Fourier-transform microwave spectroscopy has been used to probe the products resulting from the reaction between CH3CHOO and water. The hydrogen-bonded complex between CH3CHOO and water together with the reaction product, hydroxyethyl hydroperoxide, were observed in the discharged plasma of a CH3CHI2/O-2/water gas mixture. The experimentally determined rotational parameters support the identification of the complex between water and the syn-CH3CHOO conformer and two conformers of hydroxyethyl hydroperoxide, produced from the anti-CH3CHOO conformer and water. Published by AIP Publishing.