Ok. Abouzied et al., S-2-S-0 SPECTROSCOPY OF THE VAN-DER-WAALS COMPLEXES OF AZULENE WITH RARE-GASES, Journal of physical chemistry, 100(11), 1996, pp. 4375-4381
The S-2-S-0 fluorescence emission and excitation spectra of jet-cooled
azulene and its complexes with the rare gases, Ne, Ar, Kr, and Xe, ha
ve been measured. Features due to AZ . RG(n) (n = 1-4 when RG = Ar, Kr
, Xe and n = 1 when RG = Ne) are observed in the S-2-S-0 fluorescence
excitation spectra when azulene is coexpanded with the rare gases. The
microscopic solvent shifts, delta (v) over bar, of the origin bands f
or each complex scale linearly with the polarizability of the adatom(s
), indicating that binding is dominated by dispersive interactions. Th
is conclusion has been confirmed in calculations of the separate contr
ibutions of dispersion and induction to delta (v) over bar. Mildly anh
armonic progressions in very low frequency excited-state intermolecula
r (van der Waals) modes are attached to the origin bands of each AZ .
Kr-n and AZ . Xe-n complex. The dominant progression is assigned to si
ngle quantum changes in that excited-state bending mode which involves
motion of the adatom(s) in the plane perpendicular to the azulene rin
g containing the long (x) axis of the molecule. This assignment has be
en confirmed by calculating the frequencies of the bending and stretch
ing vibrations in the ground state by using one-dimensional Morse and
Taylor's series potential functions. The most stable geometries of the
n = 1-4 complexes in their ground states have been calculated by usin
g a summation of pairwise atom-atom Lennard-Jones 6-12 potentials. The
potential minima of the 1:1 complexes are located over the seven-memb
ered ring; no second minimum is found over the five-membered ring. The
most stable 1:2 species appears to be the symmetric (1 + 1) complex i
n which one adatom is bound on each side of the azulene surface. Some
evidence of the asymmetric (2 + 0) isomer is also found.