electronic spectroscopy of dcf
DESCRIPTION
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 53201-1881. - PowerPoint PPT PresentationTRANSCRIPT
Electronic spectroscopy of DCFElectronic 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 53201-1881
60th International Symposium on Molecular Spectroscopy
Ene
rgy
HCF: A case study for the RT effect
HCF represents a case of the Renner-Teller (RT) effect whereboth 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 theRT interaction.
In HCF, the two singlet states correlate with 1 in the linearconfiguration.
X1A
Ã1Aã3A
HCF: A case study for the RT effect
0
20
40
60
80
100
120
140
0 2 4 6 8
2'
A r
otat
iona
l con
stan
t in
cm-1
(1,n,0)
(0,n,0)
(0,n,1)
0
1
2
3
4
5
6
7
8
9
0 1 2 3 4 5 6 7 8
2'L
ifetim
e in
ms
K=0
K=1
K=2
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
Building upon our previous studies of HCF, we wish to probe the spectroscopy and dynamics of the Renner-Teller effect in DCF using: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 SpectroscopyFluorescence Excitation Spectroscopy
Fluorescence lifetime measurementsFluorescence lifetime measurements
Polarization Quantum Beat spectroscopyPolarization Quantum Beat spectroscopy
Determine excited state barriers to linearity and dissociationDetermine excited state barriers to linearity and dissociation Compare our results with high level electronic structure calculationsCompare our results with high level electronic structure calculations
Objectives of the present work
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
GHV
laser
Fluorescence excitation spectrum of DCF: (0,0,0)
K
01
2
01
2
Trot ~ 15 K17280 17300 17320 17340 17360 17380 17400 17420
Simulation
Inte
nsity
wavenumber (cm-1)
Experiment
3
Fluorescence excitation spectra of (0,2,0) states
2 = 5
3
2
1
0
-20 0 20 40 60 80 100 120
wavenumber relative to band origin (cm-1)
4
Variation in A rotational constant with quanta of bend for à state
The A constant increases dramatically with bending excitation, signifying the approach to linearity
a
A Ia-1
small A
large A
0 1 2 3 4 5 6
15
20
25
30
35
40
2
A c
onst
ant
in c
m-1
Variation in vibrational intervals for pure bending states (0,2,0), K = 0
“Dixon dip” occurs at barrier to linearity
0 2 4 6 8
720
730
740
750
760
770
780
790G
(2+
1)-
G(
2)
Dixon plot of vibrational intervals for pure bending states (0,2,0), 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)
22000 23000 24000 25000 26000
724
726
728
730
732
734
736
738
740
742
G(
+1
)-G
( )
0.5*[G()+G(+1)]
E = 6660 cm-1
à state vibrational parameters for HCF and DCF
Parameter
HCF
(in cm-1)
DCF
(in cm-1)
2784.9(24) 2113.6(16)
´ 1029.9(8) 792.1(2)
´ 1270.8(17) 1254.0(5)
x12´ - 36.6(6) - 15.1(4)
x22´ - 7.5(2) - 4.54(3)
x23´ - 10.0(10) - 16.3(8)
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 à 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)
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
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