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34 pags., 15 figs., 3 tabs., Carbonyl oxides, RRCOO, 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 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., This research was supported by JSPS KAKENHI Grant Nos. 19205002 (Y.E.), 25410004 (M.N. and Y.E.) and 15K05378 (M.N.) and by the Ministry of Science and Technology of Taiwan under Grant Nos. MOST 104-2113-M-009-020 (Y.E.) and MOST 105-2811-M-009-026 and 106-2811-M-009- 023 (C.C.).

The 101–000 and 202–101 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 Δ 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.

Pure rotational transitions of the anti-form of the simplest alkyl-substituted Criegee intermediate, anti-CH3CHOO, were observed by Fourier-transform microwave spectroscopy. The observed transition frequencies in the A and E levels of the ground vibrational state were analyzed together, and molecular constants including parameters which characterize the internal rotation of the methyl rotor were determined. The experimentally determined barrier height of the three-fold potential for the methyl internal rotation is 399.1 cm−1, less than a half of that of the other conformer, syn-CH3CHOO (Nakajima and Endo, 2014).

Pure rotational transitions of the simplest Criegee intermediate, CH2OO, were observed for several excited vibrational levels by Fourier-transform microwave spectroscopy combined with a double-resonance technique, and precise rotational constants of vibrationally excited CH2OO were determined. Comparing the experimentally determined vibration–rotation constants with those derived from a high-level ab initio potential energy surface, vibrational assignments were made for the observed levels. The observed intensities of the 101–000 rotational lines suggested that the COO bending mode is significantly excited.

Pure rotational transitions of weakly bound complexes of the simplest Criegee intermediate CH2OO with Ar, CO, and N2 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.

Electronic excitation spectra of the B 2 A ″ - X 2 A ″ transition of the trans-2-methylvinoxy radical were observed in the region of 29 000–32 000 cm−1 by laser-induced fluorescence and fluorescence depletion spectroscopy. Fourteen vibronic bands observed in the depletion spectrum were unambiguously identified to be originating from the radical. Dispersed fluorescence spectra from three different vibronic levels were also obtained, and a total of 69 emission bands were assigned, yielding the ground state vibrational constants.

Gas phase excitation and emission spectra of three naphthylmethyl radical chromophores are presented. These resonance-stabilized species, 1-naphthylmethyl, 2-naphthylmethyl, and α-acenaphthenyl, each possessing an sp(2) carbon adjacent to a naphthalene moiety, are studied by resonant two-color two-photon ionization, laser induced fluorescence, and dispersed fluorescence spectroscopy. Identification of the radicals is made through a combination of dispersed fluorescence and density functional theory calculations. All three species possess spectra in the 580 nm region. The possible relevance to unidentified spectroscopic features such as the diffuse interstellar bands and emission from the Red Rectangle nebula is discussed.

The electronic spectrum of the jet-cooled 1-indanyl radical has been identified in the products of a hydrocarbon discharge in argon. Electronic excitation spectra were observed in the region 20800-22600 cm(-1) by resonant two-color two-photon ionization and laser-induced fluorescence spectroscopies. In addition to the new spectrum at m/z = 117, the spectrum of 1-phenylpropargyl was also observed strongly, as was an unidentified spectrum carried by m/z = 133. The origin band of the 1-indanyl A2A''-X2A'' band system was observed at 21159 cm(-1) with the ionization potential of the radical experimentally determined to be 6.578 +/- 0.001 eV from a photoionization efficiency spectrum. Single vibronic level fluorescence was dispersed to determine the ground state vibrational frequencies that were utilized to confirm the identity of the radical in comparison with quantum chemical calculations. The calculated ground state frequencies and ionization potential, along with a calculated dispersed fluorescence spectrum of the origin band for the 1-indanyl radical, all provide a positive chemical identification.

The cis-1-vinylpropargyl (cis-1VPR, cis-pent-4-en-1-yn-3-yl) and trans-1-vinylpropargyl (trans-1VPR, trans-pent-4-en-1-yn-3-yl) radicals, produced in a supersonically cooled hydrocarbon discharge, have been identified by a synergy of 2-dimensional fluorescence and ionization spectroscopies, revealing their electronic origin transitions at 21,232 and 21,645 cm(-1) respectively. These assignments are supported by an excellent agreement between calculated ground state frequencies of cis-1VPR and trans-1VPR with those obtained by dispersed fluorescence spectroscopy. In addition, high-resolution rotational contours of the two bands are well simulated using calculated X- and A-state trans-1VPR and cis-1VPR rotational constants. Finally, computed origin transition energies of these two isomers are within several hundred wavenumbers of the observed band positions. With the 1-phenylpropargyl radical, the 1VPR isomers are the second 1-substituted propargyl species to have been observed abundantly from a hydrocarbon discharge, while no 3-substituted analogue has been positively identified. This is likely due to the greater resonance stabilization energy of the 1-substituted species, arising from concerted delocalization of the unpaired electron over the vinyl and propargyl moieties.

The rate constants for the reactions of C2(X1Sigma(g)+) with H2 and D2 have been investigated experimentally and theoretically to assess the statistical theory of the reaction and to reveal the mechanism of the reaction. The ground-state C2 radicals were generated by multiphoton laser-photolysis of C2Cl4 at 248 nm and were probed by a laser-induced fluorescence method using the Mulliken system (D1Sigma(u)+-X1Sigma(g)+). Rate constants have been measured to be k[C2(X)+H2] = 5.6 x 10(-11) exp[-9.1 (kJ mol(-1))/RT] and k[C2(X)+D2] = 3.2 x 10(-11) exp[-9.9 (kJ mol(-1))/RT] cm3 molecule(-1) s(-1) in the temperature range 293-395 K and at total pressure around 10 Torr (He buffer). Quantum chemical calculations at the MRCI level revealed that the reaction predominantly proceeds via a collinear direct-abstraction transition state. The measured rate constants as well as the kinetic isotope effect were well reproduced by the transition-state theory based on the MRCISD+Q/aug-cc-pV5Z calculations, provided that the anharmonic bending vibrations of the transition states were properly treated. The effect of the Davidson correction was found to be significant for the potential energy surface around the early transition state.

The gas-phase laser-induced fluorescence (LIF) spectrum of a 1-phenylpropargyl radical has been identified in the region 20,800-22,000 cm(-1) in a free jet. The radical was produced from discharges of hydrocarbons including benzene. Disregarding C2, C3, and CH, this radical appears as the most strongly fluorescing product in a visible wavelength two-dimensional fluorescence excitation-emission spectrum of a jet-cooled benzene discharge. The structure of the carrier was elucidated by measurement of a matching resonant two-color two-photon ionization spectrum at m/z = 115 and density functional theory. The assignment was proven conclusively by observation of the same excitation spectrum from a low-current discharge of 3-phenyl-1-propyne. The apparent great abundance of the 1-phenylpropargyl radical in discharges of benzene and, more importantly, 1-hexyne may further underpin the proposed importance of the propargyl radical in the formation of complex hydrocarbons in combustion and circumstellar environments.

A laser-induced fluorescence excitation spectrum of the cyclohexadienyl ( c -C 6 H 7 ) radical was observed in the region between 550 and 530 nm under jet-cooled conditions. A partly rotationally resolved spectrum of the vibronic origin band was obtained with a high-resolution laser scan. The observed rotational structure of the origin band is that of a b -type transition, being not discrepant with the A ∼ 2 A 2 – X ∼ 2 B 1 electronic transition which has been indicated by a few theoretical calculations. The origin band position and the rotational constants in the upper and lower states were determined from a rotational analysis of the spectrum. The determined molecular constants agreed very well with results of our ab initio calculations. The theoretical vibrational frequencies for the upper and lower electronic states were also calculated for comparison with the experimental results.

We observed microwave absorption spectra of some deuterated benzenes and accurately determined therotational constants of all H/D isotopomers in the ground vibrational state. Using synthetic analysis assuming that all bond angles are 120°, the mean bond lengths were obtained to be r[0](C–C) = 1.3971 Å and r[0](C–H) =r[0](C–D) = 1.0805 Å. It has been concluded that the effect of deuterium substitution on the molecular structureis negligibly small and that the mean bond lengths of C–H and C–D are identical unlike small aliphatic hydrocarbons, in which r[0](C–D) is about 5 mÅ shorter than r[0](C–H). It is considered that anharmonicity is very small in the C–H stretching vibration of aromatic hydrocarbons.

The Ã(2)Σ(+)-X̃(2)Πi band system of l-SiC3H in the region 14,700-16,300 cm(-1) was re-investigated by laser induced fluorescence (LIF) and fluorescence depletion spectroscopy. Rotational analyses were made for three intense bands 0(0)(0), 4(0)(1), and 6(0)(1)7(0)(1) by observing high-resolution LIF excitation spectra. The determined rotational constants demonstrate that SiC3H is linear in the à state, as is the case in the X̃ state, and the observed band types are consistent with the vibrational assignments. The ν3(″) (C1-C2 stretch) level was identified in a newly observed dispersed fluorescence spectrum from the zero-vibrational level of the à state.

In a discharged supersonic jet of carbon disulfide, a band system of a new species is observed by laser-induced fluorescence (LIF) spectroscopy. Rotationally resolved spectra show that the observed electronic transition is 2Π3/2–2Π3/2. Since both sulfur and carbon atoms have even numbers of electrons, it is concluded that the spectral carrier is an ionic species. Furthermore, the spectral carrier is confirmed to have two equivalent carbon atoms from the LIF spectra of the 13C-substituted species. With a help of ab initio calculations, the carrier is identified as the linear negative ion SCCS−, where the observed electronic transition is considered to be A 2Πg–X 2Πu. A mass spectrometric measurement also gives evidence that SCCS− is produced in the discharged jet. The vibrational structure for the upper electronic state is determined by both LIF and fluorescence depletion spectroscopy. A dispersed fluorescence spectrum is also observed to determine the vibrational structure of the lower electronic state. ...

Pure rotational transitions of the NCCS radical, showing resolved fine and hyperfine splittings, have been observed by Fourier-transform microwave spectroscopy in a discharged supersonic jet of acetonitrile and carbon disulfide. Since the transitions have been observed at frequencies corresponding to the even multiples of the rotational constant, it is concluded that the NCCS radical has a bent structure in the ground electronic state, X 2A′, and the Ka=0 ladder of the radical has been observed under the jet-cooled condition. Precise molecular constants, including the hyperfine constants of the nitrogen nucleus, are determined by a least-squares fit for the observed transition frequencies using a standard asymmetric top Hamiltonian. The determined rotational constant is compared with results of high-level ab initio calculations in order to confirm the spectral carrier to be the bent NCCS radical.

Laser-induced fluorescence spectrum of the A 3Πi←X 3Σ− transition of the CCS radical has been studied in a discharged supersonic jet of a mixture gas, carbon disulfide and acetylene diluted in Ar. More than 40 vibronic bands in the 600–925 nm region have been assigned to the transitions from the ground vibronic level of the CCS radical. The progression of the C–C stretching mode was identified for υ1=1–4, and the harmonic frequency of the mode was determined to be 1840.13(1) cm−1. In addition to the perpendicular bands, Σ–Σ parallel-type bands have been observed and assigned to vibronically forbidden transitions, A(υ1,0,1)←X(0,0,0). Based on the positions of the bands, the harmonic frequency and the Renner parameter of the bending mode in the A 3Πi state were determined to be 399.00(3) cm−1 and −0.234 67(7), respectively. High-level ab initio calculations were performed to compare the results with the experimentally determined vibronic parameters. Since the band at 778 nm has a complicated rotational st...

Laser-induced fluorescence (LIF) excitation spectra of the SiH 2 A (1,0,0) – and A (1,1,0)–X (0,0,0) bands, and dispersed fluorescence (DF) spectra from the A (1,0,0) and (1,1,0) levels were measured in the supersonic-free jet. From the rotational structures of the excitation spectra, the rotational constants in A (1, v 2 ,0), v 2 =0∼2, were determined. The fluorescence decay profiles of the single ro-vibronic levels were also measured, and the fluorescence lifetimes were determined. Based on the lifetimes, it was found that the predissociation depending on the vibronic level starts between the A (1,4,0) and (1,5,0) levels, and the predissociation depending on the rotational level in the A state is suppressed by the ν 1 mode excitation and is promoted by the ν 2 mode. The latter one is qualitatively explained by considering a second-order predissociation mechanism and a rotation-vibration constant, α i A .

New vibronic bands were observed in the 17 000–17 600 cm −1 region by laser induced fluorescence (LIF) spectroscopy in the discharged products of a mixture of C2H2 and CS2 in a supersonic jet. The effective rotational constants and the position of the vibronic band origin have been determined to be B ″ eff =0.01910(2) cm −1 , B ′ eff =0.01891(2) cm −1 , and T 0 =16961.5161(5) cm −1 , respectively. The spectral carrier of the bands has been confirmed to be the HC6S radical from the chemical behavior of the products and the determined rotational constant.

Vibronic band systems for the HC 4 S and DC 4 S radicals were observed in supersonic jets for the first time by laser induced fluorescence (LIF) spectroscopy. The rotational structures of the bands were resolved by high-resolution scans. It was found that all the observed bands are 2 Π 3/2 – 2 Π 3/2 transitions. Band origins and effective rotational constants of the origin bands are determined to be T 0 =19 980.687(1) and B ′ eff =0.046580(4) cm −1 for HC 4 S, T 0 =20 034.8748(9) and B eff ′ =0.044294(3) cm −1 for DC 4 S. Ab initio calculations were carried out to interpret the vibronic transitions.

Two silicon-bearing carbon chain radicals, SiC2N and SiC3N, were detected in the laboratory by Fourier transform microwave spectroscopy. Molecular constants including the hyperfine coupling constants have been determined for the two radicals in the ground electronic states. The SiC2N and SiC3N radicals have linear structures in the (2)Π ground electronic states with inverted and regular fine structures, respectively, as are the cases for their isoelectronic radicals, SiC3H and SiC4H, indicating that the SiC(n)N radicals have similar electronic structures to the SiC(n +1)H radicals. The electronic structures of SiC2N and SiC3N in the ground states are discussed on the basis of the experimentally determined molecular constants.

BACKGROUND The c-met and the c-erb B-2 protooncogenes belong to a family of tyrosine kinase growth factor receptors. Abnormalities of these oncogenes and protein products have been reported in several cancers. The authors investigated the correlation between clinical factors and amplification or overexpression of the c-met and/or c-erb B-2 gene in Japanese patients with gastric carcinoma patients, with a focus on prognostic significance. METHODS Amplification and overexpression of c-met and c-erb B-2 were investigated retrospectively in 128 gastric carcinoma patients by using immunohistochemistry and Southern blot hybridization. Survival analysis was performed with the Kaplan–Meier test, and the log rank test was used for statistical analysis. RESULTS Overexpression of c-met and c-erb B-2 was observed in 46.1% and 16.4% of gastric carcinoma cases, respectively. Gene amplification of c-met and c-erb B-2 was detected in 10.2% and 11.7% of gastric carcinoma cases, respectively. Amplification and overexpression of c-met were correlated significantly with depth of tumor invasion and lymph node metastasis, whereas amplification and overexpression of c-erb B-2 were correlated significantly with histologic type. The survival rate of patients with amplification and/or overexpression of c-met or c-erb B-2 was significantly poorer than that of patients with no amplification or overexpression. Multivariate analysis revealed that c-met overexpression and lymph node metastasis were independent prognostic factors. CONCLUSIONS These data suggest that overexpression and/or gene amplification of c-met and c-erb B-2 may be prognostic factors in gastric carcinoma. Cancer 1999;85:1894–902. © 1999 American Cancer Society.

In order to examine significant roles of conformations played in various research fields, a molecule with two internal-rotation axes of high symmetry, 1,4-pentadiene, was studied in detail through the observation of its rotational spectra by using various types of microwave spectroscopy, Stark modulation and Fourier transform in the centimeter-wave region, direct absorption in the millimeter-wave region, and centimeter-/millimeter-wave combinations for double resonance, along with ab initio molecular orbital calculations. The molecule was confirmed to exist in three rotameric forms: skew-skew, cis-skew, and skew-skew'. For the cis-skew form, rotational spectra not only in the ground vibrational state, but also in three excited C-C torsional states were detected. Rotational and centrifugal distortion constants were precisely determined by the analysis of all the observed spectra, in addition to the relative energies of the three isomers and the torsional frequencies for the cis-skew form, as estimated from the observed spectral line intensities. The skew-skew form was found to be the most stable among the three isomers, the cis-skew form higher in energy than the skew-skew by 172 ± 66 cm(-1), and the skew-skew' form higher in energy than the cis-skew by 44 ± 26 cm(-1). These experimental results were compared with those derived from a two-dimensional potential energy surface calculated by ab initio molecular orbital methods, in order to obtain a global view of molecular dynamics taking place on the surface, while paying attention to unique features of internal rotation characteristic of two dimensions.

Pure rotational transitions of the dimethyl-substituted Criegee intermediate (dimethyl carbonyl oxide, acetone oxide), (CH3)2COO, were observed in the discharge plasma of a C(CH3)2I2/O2 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.

The spectra of 1-indanyl-based resonance-stabilized radicals containing a hydroxyl group are identified in an electrical discharge containing indene and its alkylated derivatives. It is argued that such species form by addition of a discharge-nascent hydroxyl radical, formed from trace water, to the π bond on the five-membered ring of the parent molecule. The spectral carriers are identified by analysis of their excitation and emission spectra guided by the results from quantum chemical calculations. All three hydroxylated radicals are found to exhibit origin bands in the 21300 cm(-1) region: the 2-hydroxy-indan-1-yl radical at 21364 cm(-1), the 2-hydroxy-2-methyl-indan-1-yl radical at 21337 cm(-1), and the 2-ethyl-2-hydroxy-indan-1-yl radical exhibiting two origins of similar intensity at 21287 and 21335 cm(-1).

Electronic spectra of the B̃-X̃ transition of the 1-methylvinylthio radical were observed in a discharged jet of propylene sulfide by laser-induced fluorescence spectroscopy. Identification of the spectral carrier was made by comparing the observed spectra with results of molecular orbital calculations, in particular, for vibrational frequencies, rotational contour simulations, and the Franck-Condon simulations. Vibrational structures observed in the electronic spectra indicate that the 1-methylvinylthio radical can be regarded as a molecule with C(s) symmetry at the zero-point levels of both the excited and ground states.

The D(1)((2)A("))-D(0)((2)A(")) electronic transition of the resonance-stabilized 1-phenylpropargyl radical, produced in a jet-cooled discharge of 3-phenyl-1-propyne, has been investigated in detail by laser-induced fluorescence excitation and dispersed single vibronic level fluorescence (SVLF) spectroscopy.The transition is dominated by the origin band at 21,007 cm(-1), with weaker Franck-Condon activity observed in a(') fundamentals and even overtones and combinations of a(") symmetry. Ab initio and density functional theory calculations of the D(0) and D(1) geometries and frequencies were performed to support and guide the experimental assignments throughout. Analysis of SVLF spectra from 16 D(1) vibronic levels has led to the assignment of 15 fundamental frequencies in the excited state and 19 fundamental frequencies in the ground state; assignments for many more normal modes not probed directly by fluorescence spectroscopy are also suggested. Duschinsky mixing, in which the excited state normal modes are rotated with respect to the ground state modes, is prevalent throughout, in vibrations of both a(') and a(") symmetry.

The first optical spectrum of an isolated polycyclic aromatic hydrocarbon large enough to survive the photophysical conditions of the interstellar medium is reported. Vibronic bands of the first electronic transition of the all benzenoid polycyclic aromatic hydrocarbon hexa-peri-hexabenzocoronene were observed in the 4080-4530 Angstrom range by resonant 2-color 2-photon ionization spectroscopy. The strongest feature at 4264 Angstrom is estimated to have an oscillator strength of f=1.4x10^-3, placing an upper limit on the interstellar abundance of this polycyclic aromatic hydrocarbon at 4x10^12 cm^-2, accounting for a maximum of ~0.02% of interstellar carbon. This study opens up the possibility to rigorously test neutral polycyclic aromatic hydrocarbons as carriers of the diffuse interstellar bands in the near future., 9 pages, 1 figure. Fixed a typo on the frequency of the 'b' band

The rate constants for the reactions of OH radicals with benzene and toluene have been measured directly by a shock tube/pulsed laser-induced fluorescence imaging method at high temperatures. The OH radicals were generated by the thermal decomposition of nitric acid or tert-butyl hydroperoxide. The derived Arrhenius expressions for the rate constants were k(OH + benzene) = 8.0 x 10(-11) exp(-26.6 kJ mol(-1)/RT) [908-1736 K] and k(OH + toluene) = 8.9 x 10(-11) exp(-19.7 kJ mol(-1)/RT) [919-1481 K] in the units of cubic centimeters per molecule per second. Transition-state theory (TST) calculations based on quantum chemically predicted energetics confirmed the dominance of the H-atom abstraction channel for OH + benzene and the methyl-H abstraction channel for OH + toluene in the experimental temperature range. The TST calculation indicated that the anharmonicity of the C-H-O bending vibrations of the transition states is essential to reproduce the observed rate constants. Possible implications to the other analogous H-transfer reactions were discussed.

The hydrogen-bonded complex between water and the simplest Criegee intermediate CH2OO was detected by Fourier-transform microwave spectroscopy under a jet-cooled condition. Both a-type and b-type rotational transitions were observed for H2O-CH2OO and D2O-CH2OO. The determined rotational constants enable us to conclude that the complex has an almost planar ring structure with the terminal oxygen atom of CH2OO being a strong proton acceptor.

Pure rotational transitions of the Ar-CS van der Waals complex have been observed by Fourier Transform Microwave (FTMW) and FTMW-millimeter wave double resonance spectroscopy. Rotational transitions of v(s) = 0, 1, and 2 were able to be observed for normal CS, together with those of C(34)S in v(s) = 0, where vs stands for the quantum number of the CS stretching vibration. The observed transition frequencies were analyzed by a free rotor model Hamiltonian, where rovibrational energies were calculated as dynamical motions of the three nuclei on a three-dimensional potential energy surface, expressed by analytical functions with 57 parameters. Initial values for the potential parameters were obtained by high-level ab initio calculations. Fifteen parameters were adjusted among the 57 parameters to reproduce all the observed transition frequencies with the standard deviation of the fit to be 0.028 MHz.

Pure rotational spectra of the allenyloxy radical (CH2=CCHO) were observed by Fourier transform microwave (FTMW) and FTMW-millimeter wave double-resonance spectroscopy. Molecular constants including the hyperfine interaction constants of CH2=CCHO in the (2)A(″) ground electronic state were precisely determined. Ab initio calculations indicate that CH2=CCHO has a linear C-C-C backbone with Cs symmetry, where the formyl group is in the Cs plane and perpendicular to the methylene group. The determined rotational constants and the inertial defect agree well with those derived from the calculations, implying that the calculated molecular structure is reasonable. The fine and hyperfine constants also agree with those derived from the calculated spin density, where the unpaired electron is located mainly on the central carbon atom. The ground state CH2=CCHO can, thus, be described as taking the formylvinyl (CH2=Ċ-CH=O) form rather than as the allenyloxy (CH2=C=CH-Ȯ) form.

Higher vibrational levels of the C2 molecule than those observed so far were investigated for the X(1)Σ(g)(+), A(1)Π(u), a(3)Π(u), c(3)Σ(u)(+), and d(3)Π(g) states through the Phillips, Swan, and d(3)Π(g)-c(3)Σ(u)(+) band systems under a jet-cooled condition. The term values and the molecular constants for 21 new vibronic levels were determined from rotationally resolved excitation spectra. The determined term values and rotational constants were compared to those derived from high-level ab initio potential curves. Perturbations identified in low J levels of the d(3)Π(g) (v = 8) state are most likely to be caused by the 1(5)Π(g) (v = 3) state.

The simplest Criegee intermediate CH2OO was detected in a discharged supersonic jet of a CH2Br2 and O2 gas mixture by Fourier-transform microwave spectroscopy. The experimentally determined rotational constants of CH2OO and its isotopologues enabled us to derive the geometrical structure. The determined OO and CO bond lengths, which are relevant to a discussion on its electronic structure, are 1.345(3) and 1.272(3) Å, respectively. The CO bond length is close to that of a typical double bond and is shorter than that of the OO bond by 0.07 Å, indicating that CH2OO has a more zwitterionic character H2C = O(⊕)-O(⊖) than biradical H2Ċ-O-O.

Pure rotational spectra of the H2O-trans-HOCO complex have been observed by Fourier transform microwave (FTMW) spectroscopy and millimeter-wave FTMW double resonance spectroscopy. The complex was produced in a supersonic jet by discharging a mixture gas of CO and H2O diluted in Ar. The observed rotational lines consist of two groups of transitions with different hyperfine patterns. This is explained by considering the internal rotation of the H2O monomer in the complex. The molecular constants including the fine and hyperfine coupling constants have been determined for the two groups of lines. The hydrogen bond distance between H2O and the trans-HOCO monomer has also been determined with other structural parameters fixed to ab initio values. The hydrogen bond distance, 1.794 Å, is much shorter than that of the water dimer, and similar to those of water-acid complexes. The Fermi coupling constant of the proton of HOCO is compared with that of the trans-HOCO monomer, leading to the conclusion that there is an induced effect on the spin density on the proton of HOCO by the complex formation.

We investigated the reactivity of O((1)D) towards two types of hydrogen atoms in CH(3)OH. The reaction was initiated on irradiation of a flowing mixture of O(3) and CD(3)OH or CH(3)OD at 248 nm. Relative vibration-rotational populations of OH and OD (1 ≤ v ≤ 4) states were determined from their infrared emission recorded with a step-scan time-resolved Fourier-transform spectrometer. In O((1)D) + CD(3)OH, 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((1)D) + CH(3)OD, 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((1)D) inserts into the C-H and O-H bonds of CH(3)OH to form HOCH(2)OH and CH(3)OOH, 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 HOCH(2)OH or decomposition of CH(3)OOH. The former decomposition channel of HOCH(2)OH produces vibrationally more excited OH because of incomplete intramolecular vibrational relaxation, and decomposition of CH(3)COOH 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((1)D) + CD(3)OH and CH(3)OD, 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.

A protocol is developed for the identification of discharge intermediates from complex electronic spectra. The protocol involves resonant ionisation mass spectrometry to determine the mass of the unknown carrier followed by a two-dimensional fluorescence spectrum which is used as a "map" to guide higher resolution techniques. High resolution dispersed fluorescence provides accurate ground electronic state vibrational frequencies which are then compared with theoretical calculations of frequencies and structures of a range of isomers consistent with the observed mass. The protocol is demonstrated in the first identification of the cis and trans-1-vinylpropargyl radicals as a ubiquitous radical in hydrocarbon discharges.

A new band system of C2, e Π3g−c Σ3u+ was studied by ab initio quantum chemical and experimental methods. The calculations were carried out at the multireference configuration interaction level of theory with Davidson’s correction using aug-cc-pV6Z basis set and include core and core-valence correlation as well as relativistic corrections computed with aug-cc-pCVQZ and cc-pVQZ bases, respectively. The vibrational energies and rotational constants of the upper e Π3g state were calculated from the computed ab initio potential energy curve. The ab initio results indicate that the electronic transition moment of the e Π3g−c Σ3u+ system is approximately one-half that of the Fox–Herzberg e Π3g−a Π3u system. Franck–Condon factors were calculated for both systems and used to guide experiments aimed at discovering the e Π3g−c Σ3u+ system. The e Π3g(v′=4)−c Σ3u+(v″=3) band of jet-cooled C2 was successfully observed by laser-induced fluorescence spectroscopy by monitoring the ensuing e Π3g−a Π3u emission.

Gas-phase laser excitation spectra of the jet-cooled CCS radical were observed for the 2 (3)Sigma(-)-X (3)Sigma(-) electronic transition in a discharge of a gas mixture containing acetylene and H(2)S in Ar. The observed excitation spectra show complicated rotational structures, consisting of a much larger number of rotational lines than those expected for this size of linear molecule. The excited vibronic levels emit fluorescence, the lifetime of which is much longer than that estimated theoretically, indicating that the upper levels are strongly mixed with many "dark" background levels. Dispersed fluorescence spectra from single vibrational levels of the 2 (3)Sigma(-) state show long progressions of the C-S stretching mode, enabling observations of many vibrational levels in the ground electronic state.

An electronic excitation spectrum of the B–X transition of the CH2CHS (vinylthio, thiovinoxy) radical was observed in the range of 21 800–23 400 cm−1 by fluorescence depletion spectroscopy. Vibrational assignments for the depletion spectrum were made with the help of a theoretical excitation spectrum computed from results of ab initio calculations. The previously observed emission spectrum [M. Nakajima et al., J. Chem. Phys. 126, 044307 (2007)] was also reassigned based on the present theoretical study. Rotational band contours observed in the depletion spectrum show a large variation due to a vibrational-level dependence of the excited state lifetime. However, no obvious vibrational mode dependence of the lifetime was observed.

A two-dimensional fluorescence (excitation/emission) spectrum of C2 produced in an acetylene discharge was used to identify and separate emission bands from the dΠg3←cΣu+3 and dΠg3←aΠu3 excitations. Rotationally resolved excitation spectra of the (4←1), (5←1), (5←2), and (7←3) bands in the dΠg3←cΣu+3 system of C2 were observed by laser-induced fluorescence spectroscopy. The molecular constants of each vibrational level, determined from rotational analysis, were used to calculate the spectroscopic constants of the cΣu+3 state. The principal molecular constants for the cΣu+3 state are Be=1.9319(19)cm−1, αe=0.01855(69)cm−1, ωe=2061.9cm−1, ωexe=14.84cm−1, and T0(c−a)=8662.925(3)cm−1. We report also the first experimental observations of dispersed fluorescence from the dΠg3 state to the cΣu+3 state, namely, dΠg3(v=3)→cΣu+3(v=0,1).

Laser-induced fluorescence (LIF) excitation spectra of the B-X (2)A(") electronic transition of the CH(2)CHS radical, which is the sulfur analog of the vinoxy (CH(2)CHO) radical, were observed under room temperature and jet-cooled conditions. The LIF excitation spectra show very poor vibronic structures, since the fluorescence quantum yields of the upper vibronic levels are too small to detect fluorescence, except for the vibrationless level in the B state. A dispersed fluorescence spectrum of jet-cooled CH(2)CHS from the vibrationless level of the B state was also observed, and vibrational frequencies in the X state were determined. Precise rotational and spin-rotation constants in the ground vibronic level of the radical were determined from pure rotational spectroscopy using a Fourier-transform microwave (FTMW) spectrometer and a FTMW-millimeter wave double-resonance technique [Y. Sumiyoshi et al., J. Chem. Phys. 123, 054324 (2005)]. The rotationally resolved LIF excitation spectrum for the vibronic origin band of the jet-cooled CH(2)CHS radical was analyzed using the ground state molecular constants determined from pure rotational spectroscopy. Determined molecular constants for the upper and lower electronic states agree well with results of ab initio calculations.

A new band system of C2, dΠg3←cΣu+3 is observed by laser induced fluorescence spectroscopy, constituting the first direct detection of the cΣu+3 state of C2. Observations were made by laser excitation of cΣu+3(v″=0) C2, produced in an acetylene discharge, to the dΠg3(v′=3) level, followed by detection of Swan band fluorescence. Rotational analysis of this band yielded rotational constants for the cΣu+3(v″=0) state: B0=1.9218(2)cm−1, λ0=−0.335(4)cm−1 and γ0=0.011(2)cm−1. The vibrational band origin was determined to be ν3−0=15861.28cm−1.

A technique for the measurements of high-temperature gas-phase chemical reactions, like those involved in combustion, has been developed and an application to OH-radical measurement has been evaluated. The developed method, shock tube/pulsed laser-induced fluorescence imaging technique, allows us to measure a quantitative concentration-time profile of radical species by a single laser pulse. The detection limit for OH radicals was as low as 1×1012moleculescm−3 at total pressures (mainly argon) of 1.5–2.4bar and temperatures of 1300–1750K, when exciting the 1-0 band of the OH A-X transition with a∼1mJ laser pulse (full width at half maximum 0.15cm−1). The applicability to time-resolved chemical kinetic measurements has been investigated by measuring the rate constants for the reaction of OH radicals with benzene (C6H6). Because of the high detection sensitivity, the initial OH-radical concentration could be kept low enough, ∼1×1013moleculescm−1, to prevent the influence of side reactions. The measured rate...