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Isopropanol is the branched isomer of normal propanol.
There are two conformers, the doubly degenerate gauche
and the singly degenerate anti, also known as trans,
which is about 120 K (or 83.4 cm–1)
higher in energy. Tunneling between the equivalent gauche
conformations lifts the degeneracy, creating a symmetric
(state number 0) and an antisymmetric (state number 1)
tunneling substate. The latter is about 46.8 GHz
above the former.
A very extensive list of transition frequencies was
taken from
(1) A. Maeda, I. R. Medvedev, F. C. De Lucia, E. Herbst,
2006 Astrophys. J. Suppl. Ser. 166, 650.
A modest number of transition frequencies were taken from
(2) E. Hirota,
1979 J. Phys. Chem. 83, 1457;
from
(3) O. N. Ulenikov, A. B. Malikova, Ch. O. Qager,
S. A. Musaev, A. A. Adilov, and M. I. Mehtiev,
1991 J. Mol. Spectrosc. 145, 262;
and from
(4) H. S. P. Müller, 2018, unpublished.
Very widespread rotation-tunneling interaction takes place
between the two gauche substates. There is no clear
evidence for rotation-tunneling interaction between anti
and either gauche substate. The Hamiltonian consists
only of even order parameters, in contrast to (1). It is
largely set up as proposed in
(5) D. Christen and H. S. P. Müller,
2003 Phys. Chem. Chem. Phys. 5, 3600.
The differences in the Hamiltonian afforded a small number
of transitions from (1) to be reassigned. In addition, a very
small number of transition frequencies with large residuals
were omitted from the fit. The signs of the lowest order
interaction parameters Fab and Fac
were chosen to be negative and positive, respectively, as in (1),
(2), and (3). Careful inspection of relative intensities in (4)
required the b-dipole component to be negative if the
a- and c-components are positive. Data from (4)
were not merged. Predicted transition frequencies with
uncertainties around 0.1 MHz should be viewed with some
caution because of the severe rotation-tunneling interaction,
those with uncertainties greater than 0.2 MHz should be
viewed with considerable caution. Nevertheless, predictions
should be sufficient for all observational purposes.
The partition functions takes into consideration only
the ground vibrational states of both conformers.
Individual contributions are available. Vibrational correction
factors should be available in the near future.
The dipole moment components were reported in (2).
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