The effect on the spectrum of electronic orbital and spin angular momentum
in triatomic molecules is being investigated in collaboration with P. R. Bunker,
W. P. Kraemer (Max Planck Institute of Astrophysics, Garching, Germany),
R. J. Buenker (University of Wuppertal) and others.
This is generally
termed the Renner effect. We have developed a computer program with which we
can calculate both the positions and intensities of the lines
in a spectrum that arise from transitions between the two halves of a
Renner state. Applications to free radicals and molecular ions are being
undertaken using potential energy surfaces calculated by ab initio methods.
We have predicted the electronic
spectra of the NH_{2}^{+} and CH_{2}^{+} ions, and these predictions will be of
assistance in their search.
For CH_{2}^{+}
it has been conjectured, on the basis of the interpretation of data obtained using
the Coulomb explosion imaging (CEI)
method, that there is a large nonadiabatic contribution to the lowlying
wavefunctions beyond that coming from the Renner effect.
Very recently,
we have calculated the energies of the lowest excited electronic
states and find, in agreement with results already in the literature, that the
excited electronic states of
CH_{2}^{+}
are at much too high an energy (greater than 6 eV)
for such nonadiabatic interaction to be significant. To compare with the CEI results
we calculate the Boltzmann averaged bending angle
distribution using our previously calculated ab initio potential
energy curves of the X,A pair of Renner interacting
potentials, and make full allowance for the Renner effect in the calculation of the wavefunctions.
This ab initio calculation leads to a distribution that is significant
over a narrower range of bending angles than that obtained experimentally by the
CEI method.
Depending on the accuracy of the CEI distribution
this could indicate an error in the ab initio potential energy surfaces.
We have modified the shape of the Xstate surface in order to approximately
reproduce the CEI result, and the change we have to make is rather large. An experimental
determination of some of the bending energy level separations for
CH_{2}^{+}
would
be a more definitive way of testing the shape of the potential surface.
The CH_{2} and HO_{2} molecules are subjects of further calculations.
Recent Publications on the Renner Effect
(108) G. Osmann, P. R. Bunker, W. P. Kraemer, and Per Jensen:
Coulomb Explosion Imaging and the
CH_{2}^{+} Molecule,
Chem. Phys. Lett., 309, 299306 (1999).
(105) G. Osmann, P. R. Bunker, Per Jensen, R. J. Buenker, J.P. Gu, and G. Hirsch:
A Theoretical Investigation of the Renner Interactions and
Magnetic Dipole Transitions in the A  X
Electronic Band System of HO_{2},
J. Mol. Spectrosc., 197, 262274 (1999).
(103) J.P. Gu, G. Hirsch, R. J. Buenker, M. Brumm, G. Osmann, P. R. Bunker and P. Jensen:
A theoretical study of the absorption spectrum of singlet CH_{2},
J. Mol. Struct., in press.
(101) G. Osmann, P. R. Bunker, P. Jensen and W. P. Kraemer: An Ab Initio
Study of the NH_{2}^{+} Absorption Spectrum. J. Mol. Spectrosc. 186, 319 (1997)
(100) G. Osmann, P. R. Bunker, P. Jensen and W. P. Kraemer: A Theoretical
Calculation of the Absorption Spectrum of CH_{2}^{+}. Chem. Phys. 225, 33 (1997).
(85) J.P. Gu, R. J. Buenker, G. Hirsch, P. Jensen and P. R. Bunker:
An ab initio calculation of the BH_{2}^{} rovibronic energies: a very small
singlettriplet splitting. J. Mol. Spectrosc. 178, 172 (1996).
(79) M. Kolbuszewski, P. R. Bunker, W. P. Kraemer, G. Osmann and P.
Jensen: An ab initio calculation of the rovibronic energies of the BH_{2}
molecule. Mol. Phys. 88, 105 (1996).
