In:
The Journal of Chemical Physics, AIP Publishing, Vol. 127, No. 19 ( 2007-11-21)
Abstract:
Two sets of 32 rotational transitions were observed for the carbon monoxide–dimethyl ether (CO-DME) complex and two sets of 30 transitions for both C13O-DME and CO18-DME, in the frequency region from 3.5to25.2GHz, with J ranging from 1←0 up to 7←6, by using a Fourier transform microwave spectrometer. The splittings between the two sets of the same transition varied from 2to15MHz, and the two components were assigned to the two lowest states of the internal rotation of CO with respect to DME governed by a twofold potential. A preliminary analysis carried out separately for the two sets of the observed transition frequencies by using an ordinary asymmetric-rotor Hamiltonian indicated that the heavy-atom skeleton of the complex was essentially planar, as evidenced by the “pseudoinertial defects,” i.e., the inertial defects, which involve the contributions of the out-of-plane hydrogens of the two methyl groups, Icc−Iaa−Ibb of −5.764(23) and −5.753(16)uÅ2 for the symmetric and antisymmetric states, respectively. All of the observed transition frequencies were subsequently analyzed simultaneously, by using a phenomenological Hamiltonian which was described in a previous paper on Ar-DME and Ne-DME [Morita et al., J. Chem. Phys. 124, 094301 (2006)] . The rotational constants thus derived were analyzed to give the distance between the centers of gravity of the two component molecules, DME and CO, to be 3.682Å and the angle between the CO and the a-inertial axes to be 75.7°; the C end of the CO being closer to the DME. Most a-type transitions were observed as closely spaced triplets, which were ascribed to the internal rotation of the two methyl tops of DME. The V3 potential barrier was obtained to be 772(2)cm−1 from the first-order Coriolis coupling term between the internal rotation and overall rotation, which is about 82% of V3 for the DME monomer, whereas the second-order contribution of the coupling to the B rotational constant led to V3 of 705(3)cm−1. By assuming a Lennard-Jones-type potential, the dissociation energy was estimated to be EB=1.6kJmol−1, to be compared with 1.0 and 2.5kJmol−1 for Ne-DME and Ar-DME, respectively.
Type of Medium:
Online Resource
ISSN:
0021-9606
,
1089-7690
Language:
English
Publisher:
AIP Publishing
Publication Date:
2007
detail.hit.zdb_id:
3113-6
detail.hit.zdb_id:
1473050-9
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