Abstract
The rotational spectrum of a 1 : 1 weakly bound complex between OCS and CS
2
has been measured by Fourier-transform microwave spectroscopy, giving ground state rotational constants of
A
= 2369.6942(9) MHz,
B
= 994.4467(6) MHz and
C
= 700.5137(3) MHz for the normal isotopic species. The experimental dipole moment components are
μ
a
= 0.2893(4) D and
μ
b
= 0.6364(27) D, with
μ
total
= 0.6991(25) D. The rotational constants and dipole moment components are consistent with a structure of
C
s
symmetry, in which the CS
2
and OCS monomers are aligned almost parallel to one another, with a center of mass separation of 3.8017(2) . This structure is in good agreement with the lowest energy geometry obtained from an
ab initio
calculation at the MP2 6-311++G(2d,2p) level which predicts rotational constants of
A
= 2322 MHz,
B
= 1036 MHz and
C
= 716 MHz and dipole moment components of
μ
a
= 0.32 D and
μ
b
= 0.69 D. Semi-empirical modeling using the ORIENT program gives similarly good agreement, although the predicted rotational constants and dipole moment are a little further from the experimental results (
A
= 2458 MHz,
B
= 1027 MHz and
C
= 725 MHz and
μ
a
= 0.34 D and
μ
b
= 0.68 D).
Theoretical and microwave spectroscopic studies give a near-parallel heavy-atom planar structure for the OCS-CS
2
weakly bound dimer.