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.

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.

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.

Weak, improper, C-O...H-C hydrogen bonds in the dimethyl ether dimer.

The ground-state rotational spectrum of the dimethyl ether dimer, (DME)(2), has been studied by molecular beam Fourier transform microwave and free jet millimeter wave absorption spectroscopies. The molecular beam Fourier transform microwave spectra of the (DME-d(6))(2), (DME-(13)C)(2), (DME-d(6))...(DME), (DME-(13)C)...(DME), and (DME)...(DME-(13)C) isotopomers have also been assigned. The rotational parameters have been interpreted in terms of a C(s) geometry with the two monomers bound by three weak C-H...O hydrogen bonds, each with an average interaction energy of about 1.9 kJ/mol. The experimental data combined with high-level ab initio calculations show this kind of interaction to be improper, blue-shifted hydrogen bonding, with an average shortening of the C-H bonds involved in the hydrogen bonding of 0.0014 A. The length of the C-H...O hydrogen bonds, r(O...H), is in the range 2.52-2.59 A.