Transcript DRS Lineshape MH10 v2.ppt

Lineshape Analysis of Dynamic
Rotational Spectra in the Presence
of Internal Angular Momentum
Brooks H. Pate, Gordon G. Brown,
and Justin L. Neill
Department of Chemistry
University of Virginia
Dynamic Rotational Spectroscopy
• Rotational Spectroscopy of Highly Vibrationally
Excited Molecules
• Intramolecular Vibrational Energy Redistribution
(IVR) Causes Time-Dependent Molecular
Structure
• These dynamics lead to frequency modulation
effects known in NMR spectroscopy (Dynamic
NMR: motional narrowing and coalescence)
New Effects Unique to Rotational Motion:
Gyroscope Dynamics from Internal Angular
Momentum
Methylbutenyne
V3 = 700 cm-1
Rotational Transitions MBEY
Transition Intensities MBEY
A Sym.
E Sym.
Kr = 0 (Gyro.)
Kr = 0 (Gyro.)
Ka = 0 (Asym.)
Ka = 0 (Asym.)
A Sym.
E Sym.
Molecular Parameters for methyl
butenyne and butynone
Inertia Ellipsoid for MBEY
H3C
*q
TOP = 59.2°
*
*
C
qRAM = 35.7°
V3 = 706 cm-1
C
C
H
Principal Axis
(Asymmetric Limit)
H2C
r Axis (Gyroscope Limit)
m
*S.L. Hsu, W.H. Flygare; J. Mol. Spec. 32 (1969) 375.
m
Inertia Ellipsoid for Butynone
*
qTOP = 62.3°
H3C
C
*
qTOP = 36.8°
*
V3 = 375 cm-1
C
C
H
Principal Axis
(Asymmetric Limit)
O
* O.L. Stiefvater, J. Sheridan; Proc. Chem. Soc. 1963 (Dec.) 368.
r Axis (Gyroscope Limit)
E-Pentenyne
H
H
H
C
H
H
H
qTOP = 15o
qRAM = 1o
BASYM = 2247 MHz
BGYRO = 2256 MHz
C = 2150.5 MHz
Z-Pentenyne
|r| = 0.234
p
FRAME
Coalescence Phenomenon
No
Reaction
Lifetime
Broadening
Frequency
Pulling
Coalescence
Narrowing
A
A
B
kf
kr
B
Increasing
Reaction Rate
Gyroscope Dynamics
C: Coalescence Parameter
Gyroscope Dynamics
C: Coalescence Parameter
N: Narrowing Parameter
(Friction)
E Pentenyne 2D IR – CPFTMW Double Resonance Scan
Gyroscope Coalescence
J = 3 -2
J=2-1
Methylbutenyne Dynamic Rotational Spectrum
IR Prepares J=0 Exclusively through P(1) Excitation
J=1-0
Vinyl Isocyanate Torsional Potential
Dynamic
Rotational
Spectroscopy
State
mixing
Rigid
rotor
Justin L. Neill: WG08
3164 cm-1 band
Monitor 202101
R(1)
Laser pumps
all three J = 21 a-type
transitions at once;
population in 101 of GS
is much greater than
that in 111 or 110, so
most of excited population
is in 202
Conclusions and Acknowledgements
• Intramolecular dynamics can be studied
through line shape analysis of the
rotational spectra of highly excited
molecules
• Dynamic spectroscopy effects not limited
to geometry changes
Funding: NSF Experimental Physical
Chemistry and NSF MRI Program
Dynamic Rotational spectrum of molecules
with sources of internal angular momentum
Methyl Butenyne
rTOT = 99.8 states/cm-1
rABOVE = 13.5
12
Butynone
rTOT = 31.4 states/cm-1
rABOVE = 12.7