1. Electronic spectroscopy of DCF
Haiyan Fan, Mihaela Deselnicu, Chong Tao, Calvin Mukarakate, Ionela Ionescu and Scott Reid*
Department of Chemistry, Marquette University, P. O. Box 1881
Milwaukee, WI
60th International Symposium on Molecular Spectroscopy

2. HCF: A case study for the RT effect
HCF represents a case of the
Renner-Teller (RT) effect where
both states have large barriers
to linearity
(Other Examples: CCl2, SiH2)
Why is this interesting?
The RT interaction is largest near
the barrier region, where the
wavefunctions overlap most strongly.
Thus, one can view the onset of the
RT interaction.
In HCF, the two singlet states
correlate with 1D in the linear
configuration.
Ã1A
ã3A
Energy
X1A q

3. HCF: A case study for the RT effect
In HCF, the onset of the barrier to linearity is observed in:
an increase of A rotational constant with bending
excitation
fluorescence lifetime lengthening for K ≥ 1, due to onset
of strong RT effects as the barrier is approached

4. Objectives of the present work
Building upon our previous studies of HCF, we wish to probe the spectroscopy and dynamics of the Renner-Teller effect in DCF using:
Fluorescence Excitation Spectroscopy
Fluorescence lifetime measurements
Polarization Quantum Beat spectroscopy
Determine excited state barriers to linearity and dissociation
Compare our results with high level electronic structure calculations

5. Experimental Details
DCF is generated from CD3F using a pulsed discharge source and probed
using laser induced fluorescence
Lifetime measurements use on-axis geometry to minimize effects
from fly-out HV G
laser

6. Fluorescence excitation spectrum of DCF: (0,0,0)3 2 1 2 1 K
Trot ~ 15 K

7. Fluorescence excitation spectra of (0,u2,0) states4 3 2 1

8. A  Ia-1 Variation in A rotational constant
with quanta of bend for à state a
A  Ia-1
small A
large A
The A constant increases dramatically with bending excitation,
signifying the approach to linearity

9. Variation in vibrational intervals for
pure bending states (0,u2,0), K = 0
“Dixon dip” occurs at barrier to linearity

10. Dixon plot of vibrational intervals for
pure bending states (0,u2,0), K = 0
Quadratic fit yields a barrier height of 6660  430 cm-1
Recent theoretical estimate: 6770 cm-1
Schmidt, et al. Chem. Phys. Lett. 292, 80 (1998)

11. Ã state vibrational parameters
for HCF and DCF

12. Probing the barrier to dissociation
The highest level observed to date using LIF is the Ka = 0
level of (1,8,0), corresponding to a vibrational energy of 8048
cm-1 above the vibrationless level of the à state
In HCF, the highest level we observed using LIF is the Ka = 1
level of (1,6,0), corresponding to a vibrational energy of
8555 cm-1 above the vibrationless level of the à state
We thus set a lower limit on the dissociation energy in the Ã
state of 8555 cm-1, which is consistent with a recent
theoretical estimate of 8955 cm-1
Schmidt, et al. Chem. Phys. Lett. 292, 80 (1998)

13. Summary and Conclusions
The Renner-Teller effect in DCF has been investigated through
fluorescence excitation spectroscopy
The onset of the barrier to linearity is observed in:
a minimum in the bending vibrational intervals
an increase of A rotational constant with bending excitation
The derived barrier height is in excellent agreement with theory

14. Acknowledgements People: Haiyan Fan (Ph.D. 2004)
Ionela Ionescu (M.S. 2004)
Eduard Ionescu (M.S. 2004)
Chris Annesley (undergrad)
Joseph Cummins (undergrad)
Matthew Bowers (undergrad)
Dr. Ju Xin (Bloomsburg U.)
Funding:
NSF
ACS/PRF