The OCS Trimer:  Isotopic Studies, Structure, and Dipole Moment

Abstract

The rotational spectra of ( 18 OCS) 3 and (O 13 CS) 3 have been assigned using a pulsed-nozzle Fourier transform microwave spectrometer. The data for these isotopic species have been combined with normal species data from a paper by Connelly et al. [Connelly, J. P., et al. Mol Phys. 1996, 88, 915] to determine the nine structural parameters of the trimer. The carbon atoms form a triangle with the axes of the monomer units roughly parallel to each other (barrel-like structure). The monomers have an antiparallel-like arrangement, with the dipole moment of one monomer opposing those of the other two monomers. The dipole moment of the complex has been measured, giving values of µ a ) 0.537(10) D, µ c ) 0.373(2) D, and µ total ) 0.653(8) D. The b component of the dipole moment was too small to determine from our data but is predicted to be about 0.02 D. The structure of (OCS) 3 has been compared with similar trimers involving linear triatomic molecules and with the OCS dimer. Semiempirical calculations have been performed on the (OCS) 3 system, and they show good qualitative agreement with the experimental structure.

( N 2 O ) 2 ⋅ SO 2 : Rotational spectrum and structure of the first van der Waals trimer containing sulfur dioxide

“…The largest Stark shifts were in the range of 600-800 kHz for several components, and the greatest c contributions were about 30-50 kHz. Although c -type transitions might be observable, we were unable to detect any after lengthy 3 30 10 481.6097 0.0053 4 31 3 22 10 527.2685 0.0124 4 40 3 31 10 613.4085 0.0005 4 22 3 13 16 5 05 9263.0436 Ϫ0.0040 6 15 5 24 10 238.2039 0.0112 6 25 5 24 10 246.1632 Ϫ0.0020 6 15 5 14 10 274.4945 0.0152 6 25 5 14 10 282.4544 0.0026 7 07 6 16 10 723.2229 Ϫ0.0016 7 17 6 06 10 723.3717 0.0013 7 26 6 25 11 715.0731 Ϫ0.0057 7 16 6 15 11 721.4729 Ϫ0.0009 7 26 6 15 11 723.0536 0.0023 8 08 7 17 12 183.9324 Ϫ0.0046 8 18 7 07 12 183.9623 0.0022…”

“…The cause of these problems involving S 18 O 2 is unknown. It is possible that 18 O and 16 O exchange readily from water present in the sample manifold or some other process may have lowered the stated enrichment.…”

“…[12][13][14][15][16][17][18] This arrangement presumably maximizes the dispersion interaction while the twisting and turning away from three parallel sticks further balances the electrostatic and repulsive interactions. These experimental results have shown good qualitative, and occasionally quantitative, agreement with structures predicted by a semiempirical model which includes electrostatic, dispersion, and repulsion terms.…”

“…The complex is the first trimer containing the bent molecule SO 2 to be studied by this technique, although many SO 2 containing dimers have been studied, 2,25-27,33-35 as have many trimers containing only linear molecules or combinations of linear molecules with rare gas atoms or occasionally water. [13][14][15][16]18,[36][37][38] Modeling with a semiempirical program that includes electrostatic, dispersion and repulsion terms was helpful in predicting a structure that was a qualitatively good approximation to the experimental configuration. This model was a useful tool in the assignment of the spectra of both the normal species and isotopomers.…”

Theory vs. experiment for molecular clusters: Spectra of OCS trimers and tetramers

“…Table IV also gives the experimental r 0 structure from Ref. 10, and the theoretical equilibrium structures from Ref. 14 and the present work, as discussed in Sec.…”