Teruhiko Ogata

Fourier‐transform microwave spectroscopy of triplet carbon monoxides, C2O, C4O, C6O, and C8O

Rotational spectra of CnO with n=2, 4, 6, and 8 have been observed by using a Fabry–Perot type Fourier‐transform microwave spectrometer cooperated with a pulsed discharge nozzle. The molecules have been generated by an electric discharge of carbon suboxide diluted in Ar, and adiabatically cooled to ≊2 K in a subsequent supersonic expansion. All the observed spectra for these species are characterized as linear molecules in the 3Σ− electronic ground state. Since all the three spin sublevels have been detected even in the free‐jet condition, the spin–spin coupling constants have been determined precisely as well as other spectroscopic constants. The coupling constants show rapid increase as n becomes larger, indicating smaller energy gaps between the excited 1Σ+ state and the 3Σ− ground state for the longer species. Along with the recent observation of singlet CnO (n=5, 7, and 9) [Ogata, Ohshima, and Endo, J. Am. Chem. Soc. (submitted)], the present study has established the existence of a complete set of t...

The microwave rotational spectrum of the Ar–CO dimer

Pure rotational spectra of four different isotopomers of the dimer Ar–CO have been investigated between 8 and 18 GHz using a pulsed beam cavity Fourier transform spectrometer. The spectra confirm that the complex is a prolate near‐symmetric rotor with an essentially T‐shaped structure, and that it undergoes large amplitude zero‐point motion. It is shown that on the average the argon is closer to the oxygen than to the carbon. The transitions measured obey a‐type selection rules with ΔJ=+1, ΔKa=0, and ΔKc=+1. For 40Ar–12C16O, transitions have been observed for Ka=0 and 1 with lower state J values of 1, 2, and 3. For 40Ar–13C16O and 40Ar–13C18O, a similar series was measured, but only for Ka=0. For 40Ar–13C17O, the 17O quadrupole hyperfine pattern was resolved in the rotational transition JKaKc = 202–101. Determinations have been made for rotational and centrifugal distortion constants, as well as for the 17O quadrupole coupling constant χaa. Effective values have been obtained for the length of the line fr...

Pure rotational spectra of the van der Waals complexes Ne–CO, Kr–CO, and Xe–CO

The pure rotational spectra of the van der Waals dimers of Ne, Kr, and Xe with CO have been measured using a pulsed jet, cavity microwave Fourier transform spectrometer. All transitions measured were a-type R-branches, obeying selection rules ΔJ=+1, ΔKa=0, and ΔKc=+1. Spectra with Ka=0 were measured for 7 isotopomers of Ne–CO, 13 of Kr–CO, and 17 of Xe–CO. Transitions with Ka=1 were measured for 20Ne–12C16O and 84Kr–12C16O. Rotational constants and centrifugal distortion constants have been determined for all species, as well as the 17O quadrupole coupling constants χaa for 84Kr–13C17O and 20Ne–13C17O. Effective structural parameters have been calculated from the rotational constants. Results derived from the 17O quadrupole coupling constants and centrifugal distortion constants indicate that Ne–CO is considerably more flexible than Ar–CO, Kr–CO, or Xe–CO. Failure to observe hyperfine structure due to the 21Ne, 83Kr, and 131Xe nuclei is discussed in terms of the weak rare gas–CO bonding. Comparisons have ...

Free jet rotational spectrum and Ar inversion in the dimethyl ether–argon complex

Abstract The results of free jet millimeter-wave absorption and molecular beam Fourier transform microwave investigations of dimethyl ether–Ar are reported. The Ar atom lies in the σ v symmetry plane of dimethyl ether at a r 0 -distance of 3.58 A and the line connecting the argon atom to the center of mass ( cm ) of dimethyl ether (Ar- cm ) forms a r 0 -angle of 77° with the O- cm line. All rotational transitions are split into two component lines, due to the tunnelling of Ar from above to below the C–O–C plane. The corresponding inversion splitting has been used to determine the barrier to inversion. Some additional information on the pathways of the Ar inversion and the potential energy function have been obtained from ab initio calculations.

Microwave spectrum, barrier to internal rotation, structure, and dipole moment of 1,1,1,2-tetrafluoroethane

Abstract The microwave spectrum of CF 3 CH 2 F has been studied in the 8 to 26 GHz region, with b -type, Q - and R -branch transitions being assigned for the ground vibrational state and first excited torsional state. Relative intensity measurements give a torsional frequency of 108 ± 18 cm −1 , which lead to a barrier to internal rotation V 3 = 3.3 ± 0.8 kcal mol −1 . The dipole moments determined from the observed first-second order Stark effect are μ a = 0.411 ± 0.0009 D, μ b = 1.75± 0.22 D, and μ total = 1.80 ± 0.22 D. Observed moments of inertia suggest that the CF 3 group is not symmetrical or its axis and the CC bond are not collinear. The distance r F′⋯F′ is obtained 2.1594 ± 0.0006 A, where F′ refers to the outer plane fluorine atoms in the CF 3 group.

Microwave Fourier transform spectrum of the water-carbonyl sulfide complex

The microwave spectrum of the water-carbonyl sulfide complex H(2)O-OCS was observed with a pulsed-beam, Fabry-Perot cavity Fourier-transform microwave spectrometer. In addition to the normal isotopic form, we also measured the spectra of H(2)O-S(13)CO, H(2)O-(34)SCO, H(2) (18)O-SCO, D(2)O-SCO, D(2)O-S(13)CO, D(2)O-(34)SCO, HDO-SCO, HDO-S(13)CO, and HDO-(34)SCO. The rotational constants are B = 1522.0115(2) MHz and C = 1514.3302(2) MHz for H(2)O-SCO; B = 1511.9153(5) MHz and C = 1504.3346(5) MHz for H(2)O-S(13)CO; B = 1522.0215(3) MHz and C = 1514.3409(3) MHz for H(2)O-(34)SCO; B = 1435.9571(3) MHz and C = 1429.1296(4) MHz for H(2) (18)O-SCO, B = 1409.6575(5) MHz and C = 1397.9555(5) MHz for D(2)O-SCO; B = 1399.8956(3) MHz and C = 1388.3543(3) MHz for D(2)O-S(13)CO; B = 1409.6741(24) MHz and C = 1397.9775(24) MHz for D(2)O-(34)SCO; (B+C)/2 = 1457.9101(2) MHz for HDO-SCO; (B + C)/2 = 1448.0564(4) MHz for HDO-S(13)CO; and (B+C)/2 = 1457.9418(15) MHz for HDO-(34)SCO, with uncertainties corresponding to one standard deviation. The observed rotational constants for the sulfur-34 complexes are generally higher than those for the corresponding sulfur-32 isotopomers. The heavier isotopomers have smaller effective moments of inertia due to the smaller vibrational amplitude of the (34)S-C vibration (zero point) as compared to the (32)S-C, making the effective O-(34)S bond slightly shorter. Stark effect measurements for H(2)O-SCO give a dipole moment of 8.875(9)x10(-30) C m [2.6679(28) D]. The most probable structure of H(2)O-SCO is near C(2v) planar with the oxygen of water bonded to the sulfur of carbonyl sulfide. The oxygen-sulfur van der Waals bond length is determined to be 3.138(17) A, which is very close to the ab initio value of 3.144 A. The structures of the isoelectronic complexes H(2)O-SCO, H(2)O-CS(2), H(2)O-CO(2), and H(2)O-N(2)O are compared. The first two are linear and the others are T shaped with an O-C/O-N van der Waals bond, i.e., the oxygen of water bonds to the carbon and nitrogen of CO(2) and N(2)O, respectively.

Intermolecular hydrogen bonds, rotational spectrum, and structure of van der Waals complexes of (CH3)2O⋯CF2CH2 and (CH3)2O⋯CF2CHF

Abstract The results of molecular beam Fourier transform microwave (FTMW) investigations of the van der Waals complexes of dimethyl ether with 1,1-difluoroethene/trifluoroethene are reported. The rotational parameters of the complexes have been interpreted in terms of a Cs geometry with the two methyl groups lying out of the σv symmetry plane of complexes. The complexes are bound with three hydrogen bonds of which one is the stronger O⋯HC type and two are the weaker F⋯HC types. Some additional information on the structure and the hydrogen bond has been obtained from ab initio calculations.

Microwave spectrum, structure, and quadrupole coupling constants of 1-chloro-2,2,2-trifluoroethane

Abstract The microwave spectrum of CF 3 CH 2 Cl has been studied in the 8 to 26 GHz region, with b -type, Q - and R -branch transitions being assigned for both the ground vibrational state and first excited torsional state for 35 Cl species and ground vibrational state for 37 Cl species. The 35 Cl quadrupole coupling constants obtained are as follows: X aa = -36.21 MHz, χ bb = 4.48 MHz, and χ cc = 31.73 MHz. The structural parameters needed to reproduce the observed moments of inertia suggest that the CF 3 group is either not symmetrical or its axis and the CC bond are not collinear. The r F …F distance obtained is 2.1604±0.0006 A where F refers to the out-of-plane fluorine atoms.

Microwave spectrum, dipole moments, and structure of trifluoroallene

Abstract The microwave spectrum of F 2 CCCHF has been studied from the 8- to 26-GHz region, with c -type, Q - and R -branch transitions being assigned for the ground vibrational state. The rotational constants obtained are: A = 9360.050(5) MHz, B = 1739.1516(6) MHz, and C = 1554.2665(5) MHz. The dipole moments determined from the Stark effect are: μ a = 0.510(6) D, μ c = 1.40(3) D, and μ total = 1.49(3) D. The molecular structure which reproduces the observed moments of inertia has been determined. The structural parameters of allene and fluorine-substituted allenes are compared. The systematic changes that occur in the structural parameters are found as the number of substituted fluorine atoms increases.

The Simplest Linear-Carbon-Chain Growth by Atomic-Carbon Addition and Ring Opening Reactions

The formation mechanism of linear-carbon-chain molecules, C n O ( n = 2 - 9), synthesized in the discharge of C 3O 2 has been investigated on the basis of detailed analyses of previously obtained FTMW spectroscopic data. The relative abundances of the C n O products determined from their rotational spectrum intensities agree with those for the C n O (+) ions. The active chemicals in the reaction system include :C and :CCO only, and the observed products exclusively consist of C n O, leading to a likely formation mechanism of the atomic-carbon addition and ring opening reaction. This formation mechanism is simple and efficient, and it is applicable not only to linear-carbon-chains but also to a wide range of carbon processes, in particular, to ultra low temperature or incomplete combustion conditions.