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We observed microwave absorption spectra of some deuterated benzenes and accurately determined the rotational 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 r0(C-C) = 1.3971 Å and r0(C-H) = r0(C-D) = 1.0805 Å. It has been concluded that the effect of deuterium substitution on the molecular structure is negligibly small and that the mean bond lengths of C-H and C-D are identical unlike small aliphatic hydrocarbons, in which r0(C-D) is about 5 mÅ shorter than r0(C-H). It is considered that anharmonicity is very small in the C-H stretching vibration of aromatic hydrocarbons. [ABSTRACT FROM AUTHOR]

The òΣ+-X²IIi 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 000, 40¹, and 60¹ 70¹ 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 X state, and the observed band types are consistent with the vibrational assignments. The v"3 (C1-C2 stretch) level was identified in a newly observed dispersed fluorescence spectrum from the zerovibrational level of the A state. [ABSTRACT FROM AUTHOR]

The òS+-X²πi 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 000, 4¹0, and 6¹07¹0 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 X state, and the observed band types are consistent with the vibrational assignments. The ν"3 (C1-C2 stretch) level was identified in a newly observed dispersed fluorescence spectrum from the zero-vibrational level of the à state. [ABSTRACT FROM AUTHOR]

Pure rotational transitions of hydroxymethyl hydroperoxide (HMHP) were observed in the discharged plasma of a CH2I2/O2/water gas mixture, where the water complex with the simplest Criegee intermediate CH2OO has been identified [M. Nakajima and Y. Endo, J. Chem. Phys. 140, 134302 (2014)]. Isotope experiments using heavy water support that the currently observed HMHP molecule was produced by the reaction of CH2OO with water vapor. The observed species was identified as the most stable conformer with the help of quantum chemical calculations. We also clarified that productions of formic acid and dioxirane are promoted by the existence of water vapor in the discharged reaction system. [ABSTRACT FROM AUTHOR]

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∏ ground electronic states with inverted and regular fine structures, respectively, as are the cases for their isoelectronic radicals, SiC3H and SiC4H, indicating that the SiCnN radicals have similar electronic structures to the SiCn+1H radicals. The electronic structures of SiC2N and SiC3N in the ground states are discussed on the basis of the experimentally determined molecular constants. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 vs = 0, 1, and 2 were able to be observed for normal CS, together with those of C34S in vs = 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. [ABSTRACT FROM AUTHOR]

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 ²A" 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=?C-CH=O) form rather than as the allenyloxy (CH2=C=CH-&Odot; ) form. [ABSTRACT FROM AUTHOR]

An alkyl-substituted Criegee intermediate syn-CH3CHOO was detected in the gas phase through Fourier-transform microwave spectroscopy. Observed pure rotational transitions show a small splitting corresponding to the A/E components due to the threefold methyl internal rotation. The rotational constants and the barrier height of the hindered methyl rotation were determined to be A = 17 586.5295(15) MHz, B = 7133.4799(41) MHz, C = 5229.1704(40) MHz, and V3 = 837.1(17) cm-1. High-level ab initio calculations which reproduce the experimentally determined values well indicate that the in-plane C-H bond in the methyl moiety is trans to the C-O bond, and other two protons are directed to the terminal oxygen atom for the most stable structure of syn- CH3CHOO. The torsional barrier of the methyl top is fairly large in syn-CH3CHOO, implying a significant interaction between the terminal oxygen and the protons of the methyl moiety, which may be responsible for the high production yields of the OH radical from energized alkyl-substituted Criegee intermediates. [ABSTRACT FROM AUTHOR]