186.21 amu
dimer vibrational frequency = 348.4
dimer force constant = 6.66 mdyne/A
References
"Optical and Raman Spectroscopy of
Mass-Selected Rhenium Dimers in Argon Matrices"
Z. Hu, Jian-Guo Dong, John R. Lombardi, D.M.
Lindsay and W. Harbisch,
J. Chem. Phys. 101,95,(1994).
Abstract
We report absorption, laser fluorescence and Raman spectra
for Re2 in an argon matrix prepared by the mass-selected ion
deposition technique. The dirhenium absorption spectrum consists of 7 band
systems (A - G) extending from the near infrared into the ultravio-let
region. For the A system (a simple vibrational progression)
we find To = 10,817(1) cm-1, we
= 317.1(5) cm-1 and wexe = 1.0(1) cm-1.
A Franck-Condon analysis of the A system intensities predicts that this
state has a smaller equilibrium internuclear distance than the ground state
(delta re = -0.073A), in violation of Badger's rule. The B system
starts at 13,250 cm-1 and consists of 4 overlapping (and possibly
perturbed) subsystems, whose average vibrational spacing is 270(11) cm-1.
The C, D, E and F systems (vibrational spacings in parentheses) are centered
at 22,300 cm-1 (210 cm-1), 24,500 cm-1
(195 cm-1), 29,150 cm-1 (175 cm-1) and
32,900 cm-1 (160 cm-1), respectively. Weak fluorescence
spectra, obtained upon laser excitation into the A system, were characterized
by vibrational progressions to the dimer ground (X) state and to a low
lying (X') state for which To = 357.6(5) cm-1 and
we = 332.3(2) cm-1. Raman and fluorescence progressions
to the ground state were observed when the B system was excited. These
data give we = 337.9(49) cm-1 for the dimer ground state in
good agreement with measurements from photodetachment spectra [J. Am. Chem.
Soc. 108, 178 (1986)]. We propose likely assignments for the low lying
electronic states of Re2 and discuss our results in terms of
the bonding in the other Group VIIB dimers, Mn2 and Tc2.
TABLE. Spectroscopic constants for dirhenium, including band
origins (X', A and B states) or centers (C - G systems) and force
constants (k in mdyne/A).
T0 we wexe k
X 0 337.9 0.1 6.26
X' 357.6 332.3 6.06
A 10,817 317.1 1.0 5.52
BI 13,251 281 4.0
C 22,300 210 2.4(2)
D 24,500 195 2.1(2)
E 29,150 175 1.7(4)
F 32,900 160 1.4(4)
G 36,100
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