Transcript cmh2006_HCCl.ppt

Hot bands in jet-cooled and ambient
temperature spectra of HCCl
Zhong Wang, Ryan Bird, Hua-Gen Yu and
Trevor Sears
Department of Chemistry
Brookhaven National Laboratory
Thanks to:
Greg Hall and other members
of the GPMD group at BNL
Brookhaven Science Associates
U.S. Department of Energy
Funding:
DOE Division of Chemical
Sciences, Office of Basic Energy
Sciences
HCCl Spectroscopy
• Singlet and triplet states, singlet lower
MRCI/aug-cc-pVTZ
basis
1A"
RCH=1.0967A
Cl
_
X1A′
H
Brookhaven Science Associates
U.S. Department of Energy
3A"
1A'
What’s New?
• Talked about HCCl two years ago
– Now, new spectra involving X (010), (001) and
(011).
– Measure vibration-rotation parameters in ground
state.
– In upper state: A(000), (010), (001)* and (011)*
– (001) and (011) new, previous assignment of
A(001) shown to be wrong
– Rescaled ab initio surfaces to account for this,
now more accurate predictions for higher states.
Brookhaven Science Associates
U.S. Department of Energy
Cuts through surfaces
• Cut along bending
coordinate, with
approx level positions
• Vibrationally excited
ground state levels
show evidence for
triplet in
perturbations.
• Upper state levels
irregular due to RTE
mixing with excited
ground state levels.
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-1
Brookhaven Science Associates
U.S. Department of Energy
-0.8 -0.6 -0.4 -0.2
cos 
0
0.2
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Experimental setup
Digital Scope
Si photodiode
amplifiers and
demodulator
RF signal
Generator
CW Probe laser
UV reflecting
dichroic
Gas flow cell
Phase
Modulator
UV reflecting
dichroic
Brookhaven Science Associates
U.S. Department of Energy
Photolysis
Laser
(000)-(010), K=1-0
Upper: jet cooled,
lower ambient
temperature.
Difficult to assign
low J-numbering in
ambient
temperature
spectrum.
Brookhaven Science Associates
U.S. Department of Energy
A(001) at 926.2
-1
cm ?
• Previously assigned to level at 987.4 cm-1
– From band at 13253 cm-1 in ambient temp
spectrum.
– Can reassign this to (011)-(001)
• Then computed levels have reasonable
anharmonicity!
– Matching the wrong (001) frequency caused the
scaled ab initio PES to have unphysical behavior.
– Calculated higher energy regions on the PES now
too.
Brookhaven Science Associates
U.S. Department of Energy
Calculated Intensities
• Absorption from X(000) results in bending progression,
no stretches except at very high energy
• From X(001), transition to A(011) is the lowest
frequency strong band. Only Q-lines assigned originally,
so no combination difference check!
Brookhaven Science Associates
U.S. Department of Energy
1
0
(001) -(011)
jet
Rotational cooling more
efficient than vibrational, so
can see hot-bands in jet
spectrum. Low-J
combination differences
confirm assignment.
37Cl
lines 1.2 cm-1 below 35Cl
ones, no change in Clstretching quantum number.
Brookhaven Science Associates
U.S. Department of Energy
Summary
• Full characterization of X (010), X (011),
[X(001)]
– For both Cl isotopes
– Partial rotational characterization of X(012).
Rotational structure normal in these levels.
Evidence for shift down in (011) energy as
predicted from T-S interaction.
• Upper state Cl-stretching frequency corrected
– Ab intio PES calculated to higher E and scaling
adjusted to match experimental measurements.
Brookhaven Science Associates
U.S. Department of Energy
Finally
Thanks to my co-workers
Ryan,
Greg,
Trevor
Zhong
Hua-Gen
Brookhaven Science Associates
U.S. Department of Energy
…and other members of the GPMD
group at BNL