Structure of the Dimethyl Ether−CO2 van der Waals Complex from Microwave Spectroscopy

Abstract

The rotational spectrum of the 1:1 weakly bound complex formed between dimethyl ether (DME) and CO2 has been assigned by Fourier transform microwave spectroscopy, leading to rotational constants of A = 5401.24(11) MHz, B = 2010.8637(17) MHz, and C = 1493.4844(15) MHz for the normal isotopic species. Measurement of rotational spectra for an additional four isotopomers has allowed a structure determination for this complex, giving a C2v geometry in which the CO2 lies in the heavy atom plane of the DME and is aligned perpendicular to its C2 axis. This orientation is supported by second moment data and a dipole moment of μa = μtotal = 1.661(6) D. The C···O distance has been determined to be 2.711(1) A. Ab initio optimizations at the MP2/6-311++G(2d,2p) level predict a C2v geometry with a C···O bond length of 2.685 A, slightly shorter than, but still in very good agreement with, the experimental value. Predicted rotational constants and dipole moment at this level of theory are A = 5379 MHz, B = 2018 MHz, C = ...