1. STUDIES OF THE PREDISSOCIATED, QUASILINEAR STATE OF
CH35Cl AND CD35Cl PROBED BY OPTICAL-OPTICAL DOUBLE RESONANCE SPECTROSCOPY
Chong Tao, Calvin Mukarakate, Scott A. Reid Department of Chemistry, Marquette University 64rd International Symposium on Molecular Spectroscopy June 24th, 2009 WF01

2. Halocarbene photochemistry is largely unexplored
Halocarbons (e.g., CFCs)
have been famously
implicated in stratospheric
ozone depletion
It is well established that
halocarbenes are produced
in the photodecomposition
of halocarbons.
To date, very little is known
about the ultraviolet
photochemistry of
halocarbenes.
Reid, El-Khoury, Tarnovsky, Ault

3. Mono- halocarbenes (CHX)
S T S S2 S2
28000
24000
20000 S1
Energy in cm-1
16000
12000
8000 T1
4000 S0
CHF CHCl CHBr CHI

4. Singlet potential energy surfaces of
CHF (CASSCF/cc-pVTZ)
B1A’ C
A1A” C
X1A’ C

5. Schematic PES along C-X bond in :CXY
Scott Kable and George Bacskay, Sydney

6. CASSCF calculations for CHCl
Eric Brown, Loyola University

7. CASSCF calculations for CHCl B state~
CASSCF(6,5)/cc-pVTZ

8. Stationary points on the CHCl PES~ ~ ~ ~

9. Optical-optical double resonance spectroscopyHV G
PUMP
PROBE
PMT
Boxcar
Probe
Boxcar
ADC
Pump

10. OODR Spectroscopy of CHF
SEP transitions
All B state levels are broadened by dissociation
B state is quasi-linear, levels labeled by (v1,v2ℓ,v3)

11. OODR Spectrum of CH35Cl CHCl (0,91,2)
By exploiting various intermediate
levels, transitions involving the
C-H stretch (1 quantum) and
C-Cl stretch (1-3 quanta) in
combination with bend are
observed
All levels above
~ cm-1 display
lifetime broadening
CHCl (0,91,2)

12. OODR Spectrum of CD35Cl CDCl (0,131,1) Linewidths are narrower than
found in CHCl
Many levels can be
rotationally
resolved
The three line pattern
at right reflects the
ΔJ = 0, ±1 selection
rule
CDCl (0,131,1)

13. Vibrational frequencies for CHCl and CDCl
in the B state ~
CH35Cl
CD35Cl
Vibration
Exp.
(cm-1)
(cm-1)a ω1
3180
2450 ω2
737
574 ω3
960
961
ω3 in cm-1 for CH35Cl: X (812), A (926), B (960)
ω1 in cm-1 for CH35Cl: X (2803), A (2980), B (3180)

14. Where is the electronic origin?
Extrapolation predicts origin to lie near cm-1

15. Linewidth Data MP4/cc-pVTZ Energies C(3P) + HCl 25900 cm-1 (barrier)
CCl(2Π) + H
29100 cm-1
(asymptote)
CH(2Π) + Cl
33100 cm-1

16. Summary
The state of CH35Cl and CD35Cl has been investigated with OODR spectroscopy
The state is quasilinear, with a very small barrier. The
electronic origin lies near 20,800 cm-1
At energies near 26,000 cm-1, the lines are broadened by a homogenous process (presumably dissociation)
This is very close to the calculated barrier for elimination of HCl on the triplet surface

17. Acknowledgements People: Scott Kable Tim Schmidt George Bacskay
Funding:
National Science
Foundation
(CHE )