Yoshio Tatamitani

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 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.

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.

Intermolecular interaction in the formaldehyde-dimethyl ether and formaldehyde-dimethyl sulfide complexes investigated by Fourier transform microwave spectroscopy and ab initio calculations.

The ground-state rotational spectra of the formaldehyde-dimethyl ether (H2CO-DME) and formaldehyde-dimethyl sulfide (H2CO-DMS) complexes have been studied by Fourier transform microwave spectroscopy. The a-type and c-type rotational transitions have been assigned for the normal and deutrated formaldehyde-containing species of both complexes. In the case of H2CO-DME, doublets were observed with the splitting 10-300 kHz, whereas no such splittings were observed for H2CO-DMS, D2CO-DME, and D2CO-DMS. The observed rotational spectra were found consistent with a structure of Cs symmetry with DME or DMS bound to H2CO by two types of hydrogen bonds: C-H(DME/DMS)---O(H2CO) and O(DME)/S(DMS)---H-C(H2CO). The R(cm) distances between the centers of mass of the component molecules in the H2CO-DME and H2CO-DMS complexes were determined to be 3.102 and 3.200 Å, respectively, which are shorter than those in most related complexes. The spectral and NBO analyses showed that H2CO-DMS has a stronger charge transfer interaction than H2CO-DME does and that the binding energy of H2CO-DMS is larger than that of H2CO-DME.

Three Intermolecular Bonds Form a Weak but Rigid Complex: O(CH3)2···N2O

The rotational spectrum of the dimethylether (DME)-N(2)O complex has been studied for the normal and three (15)N isotopomers, leading to rotational, centrifugal distortion, and nuclear quadrupole coupling constants, the molecular structure, and a binding energy of 8.4 kJ mol(-1). Here, it is shown that many DME-N(2)O-type complexes are bound with three intermolecular bonds and that the internal rotation splitting due to the methyl groups in the rotational spectrum was fixed by complexation, implying that many weak intermolecular bonds can fix the flexible motions and maintain a rigid structure. If the model we are proposing for DME-N(2)O-type complexes can be applied to biomolecules, it may give something a clue to solve the biological riddle on the dynamic character of biomolecules that have conflicting properties of being rigid and binding weakly.

DIMETHYL SULFIDE-DIMETHYL ETHER AND ETHYLENE OXIDE-ETHYLENE SULFIDE COMPLEXES INVESTIGATED BY FOURIER TRANSFORM MICROWAVE SPECTROSCOPY AND AB INITIO CALCULATION

The ground-state rotational spectra of the dimethyl sulfide-dimethyl ether (DMS-DME) and the ethylene oxide and ethylene sulfide (EO-ES) complexes were observed by Fourier transform microwave spectroscopy, and a-type and c-type transitions were assigned for the normal, S, and three C species of the DMS-DME and a-type and b-type rotational transitions for the normal, S, and two C species of the EO-ES. The observed transitions were analyzed by using an S-reduced asymmetric-top rotational Hamiltonian. The rotational parameters thus derived for the DMS-DME were found consistent with a structure of Cs symmetry with the DMS bound to the DME by two C-H(DMS)—O and one S—HC(DME) hydrogen bonds. The barrier height V 3 to internal rotation of the ”free” methyl group in the DME was determined to be 915.4 (23) cm−1, which is smaller than that of the DME monomer, 951.72 (70) cm−1,a and larger than that of the DME dimer, 785.4 (52) cm−1.b For the EO-ES complex the observed data were interpreted in the terms of an antiparallel Cs geometry with the EO bound to the ES by two C-H(ES)—O and two S—H-C(EO) hydrogen bonds. We have applied a natural bond orbital (NBO) analysis to the DMS-DME and EO-ES to calculate the stabilization energy CT (= ∆Eσσ*), which were closely correlated with the binding energy EB, as found for other related complexes.

Microwave spectrum, barrier to internal rotation of CF3, structure, and ab initio calculation of 1,1,1,2,2-pentafluoropropane

Abstract The microwave spectrum of 1,1,1,2,2-pentafluoropropane CF 3 CF 2 CH 3 (HFC 245cb) has been studied for the first time using both a Stark modulation and Fourier transform microwave spectrometer. A least-squares analysis of the observed a- and b-type transition frequencies gave rotational and centrifugal distortion constants for the vibrational ground state as follows: A=2715.9979(2) MHz , B=1831.3817(2) MHz , C=1810.6342(2) MHz , Δ J =0.112(3) kHz , Δ JK =0.033(3) kHz , Δ K =−0.0066(19) kHz, δ J =0.0030(2) kHz , δ K =−0.73(9) kHz . The barrier height to internal rotation of the CF 3 group has been determined to be V 3 =2.86±0.72 kcal / mol . A reasonable molecular structure has been derived from the observed rotational constants combining with ab initio calculation. These barrier height and structural parameters are compared with those of other related molecules.