E. Kraka et al., INTERMOLECULAR FORCES IN ARGON VAN-DER-WAALS COMPLEXES - ROTATIONAL SPECTRUM AND AB-INITIO INVESTIGATION OF AR-OXAZOLE, Journal of physical chemistry, 99(33), 1995, pp. 12466-12477
The rotational spectrum of the oxazole-argon complex has been experime
ntally studied in the microwave region between 3 and 21 GHz using a pu
lsed molecular beam Fourier transform microwave spectrometer. The rota
tional constants were found to be A = 5012.894 86(14) MHz, B = 1398.42
8 151(32) MHz, and C = 1388.952 841(31) MHz. The centrifugal distortio
n constants are D-J' = 5.524 11(28) KHz, D-JK' = 37.1990-(30) kHz, D-K
' = -35.922(28) kHz, delta(J)' = 0.026 26(21) kHz, and R'(6) = -0.000
49(19) kHz. The diagonal elements of the nitrogen quadrupole coupling
tenser were determined to be chi(aa) = 2.3032(6) MHz, chi(bb) = -4.052
6(8) MHz, and chi(cc) = 1.7494(4) MHz. With the help of supermolecular
Moller-Plesset perturbation theory at second (MP2) and fourth order (
MP4(SDTQ)) using a (14s10p2d1f)[7s4p2d1f] basis set for argon, a 6-31G
(+sd+sp) basis for oxazole, and basis set superposition corrections, s
tability (MP2, 316; MP4, 304 cm(-1)), equilibrium geometry, charge dis
tribution, and other properties of the complex were determined. Argon
adopts a position above the ring plane (Ar-ring distance: r(0), 3.46;
MP2, 3.64; MP4, 3.58 Angstrom) clearly shifted from the centrum of the
ring in the direction of the oxygen atom. The complex is predominantl
y stabilized by dispersion interactions, while the position of the arg
on atom is determined by exchange repulsion forces that direct Ar towa
rd the O atom. A new way of analyzing van der Waals complexes and pred
icting structural and other complex properties is presented. Investiga
tion of Ar-oxazole, Ar-benzene, and Ar-CO reveals that there is no cha
rge transfer between the complex partners, contrary to previous claims
made in the literature.