The structure of C2H4 clusters from theoretical interaction potentials and vibrational predissociation data

Abstract

Optimized geometries and binding energies are calculated for ethene (ethylene) dimers, trimers, and tetramers based on a pairwise additive dimer potential. From these results intermolecular frequencies and relative abundancies (catchment areas) of the different isomers are obtained and compared with the results of accurate measurements of the photodissociation upon absorption of one photon of a CO 2 laser in the region of the v7 monomer absorption band at 949 cm-~. The clusters are size selected in a scattering experiment and show for a cluster size from n = 2 to n = 6 a frequency maximum shifted by 3 cm-1 to the blue compared with the monomer. The result is explained by the predominance of chains and chain-like structures of the clusters in the photodissociation process. The chains consist of cross-like dimer sub-units.

Theoretical investigation on structural properties of ethylene clusters (C2H4)n (n⩽25)

“…Alberts et al [9] carried out ab initio calculations at the MP2 level, in which the D 2d cross form was not taken into account. Tsuzuki and Tanabe [11] calculated energies of a variety of dimer structures at the MP2/6-311G(2d, 2p) level and concluded that the D 2d structure is the most stable, in agreement with the results obtained by Ritter and Gruen [6], Chan et al [5], and Ahlrichs et al [7].…”

“…In the study by Ahlrichs et al [7], the intermolecular potential is constructed with the aid of ab initio calculations with no electron correlation effect. Tsuzuki and Tanabe [11] indicate that potentials of the ethylene dimer without the electron correlation effect are very shallow.…”

“…Some investigations on ethylene clusters were carried out [5][6][7][8][9][10][11][12][13]. Chan et al [5] examined the structure of the dimer with rotationally resolved infrared spectroscopy; from the experimental rotational constants the dimer was estimated to take the D 2d cross form shown in Fig.…”

“…Structures of the ethylene dimer, trimer, and tetramer were examined by Ahlrichs et al [7] with a pairwise additive potential which is different from the potential [8] used in the present study. The dimer takes the cross geometry with D 2d symmetry.…”

“…The model based on the pairwise potential [7] predicts the structures of the clusters for n = 2 -4. Hence no structural information is given for the n ≥ 5 clusters.…”