Chirped-pulsed FTMW Spectrum of 4-Fluorobenzyl Alcohol. Structure and Torsional Motions in the Ground Electronic State Phase. Ryan G. Bird , and David W. Pratt University of Pittsburgh Justin L. Neill and Brooks H. Pate University of Virginia
Chirped-pulsed FTMW Spectrum of 4-Fluorobenzyl Alcohol. Structure and
Torsional Motions in the Ground Electronic State Phase.
Ryan G. Bird, and David W. Pratt
University of Pittsburgh
Justin L. Neill and Brooks H. Pate
University of Virginia
Excited State Spectroscopy
• FBA electronic spectrum
• 4 band caused by 2 internal rotations
• Difficult to separate S0 and S1 barriers
• Use CP-FTMW to study S0
0.2cm-1
Methyl Internal Rotation
• Internal rotation cause perturbations– Ĥ = ĤRot + ĤInt
• Three types of rotor– High barrier, Low barrier, Asymmetric
• Difficulties in assigning spectra1
– JB95, SPCAT, XIAM
1Kleiner, I. Journal of Molecular Spectroscopy 2010, 260, 1
CP-FTMW Spectrometer
MW Synthesizer
Arbitrary Waveform Generator
Fourier Transform
Free Induction Decay
Chirped Pulse240 MHz
500 MHzDigitizer(10 Gs/s)
High Barrier: o-Toluidine
• Ĥ = ĤRot + ĤInt + ĤQuad
• ĤRot ›› Ĥint
• ĤQuad › Ĥint
• Barrier high; Tunneling splitting low
• JB95, XIAM, SPFIT
Torsion angle60 180 300
700 cm-1
+
-
Morgan, P. J.; Alvarez-Valtierra, L.; Pratt, D. W. The Journal of Physical Chemistry A 2009, 113, 13221-13226.
AE
o-Toluidine Constants
312-211
10000 avg10 MHz CP
A E
A E
A E
A E
F = 3←2
F = 4←3
F = 2←1
F = 2←2
A Band E Band
A (MHz) 3230.29(1) 3230.35(2)
B (MHz) 2188.807(1) 2188.827(2)
C (MHz) 1316.940(3) 1316.943(5)
χaa (MHz) 2.007(7) 2.02(1)
χbb (MHz) 2.05(1) 2.04(2)
χcc (MHz) -4.06(1) -4.07(2)
DJ (kHz) 0.35(8) 0.5(1)
DJK (kHz) -1.4(3) -2.0(5)
DK (kHz) -4(4) -4(7)
dJ (kHz) 0.17(5) 0.26 (7)
dK(kHz) -0.4(6) 0.5(9)
ΔI (amu Å2) -3.590 -3.586
Lines 52 53
Low Barrier: m-Toluidine
• Ĥ = ĤRot + ĤInt + ĤQuad
• ĤRot ≈ Ĥint
• Barrier low; Tunneling splitting high
• JB95, XIAM
Torsion angle60 180 300
A
E
9 cm-1
Morgan, P. J.; Alvarez-Valtierra, L.; Pratt, D. W. The Journal of Physical Chemistry A 2009, 113, 13221-13226.
m-Toluidine ConstantsXIAM
A (MHz) 3635.9(1) B (MHz) 1791.20(8)C (MHz) 1210.31(5)χaa (MHz) 2.3(6)χbb (MHz) 1.9(6)χcc (MHz) -4.2(6)DJ (kHz) 2(1)
DJK (kHz) -2(2)DK (kHz) -31(12)dJ (kHz) 0.8(5)dK(kHz) 23(7)V3 (cm-1) 4.23(6)
ΔI (amu Å2) -0.52
Lines 79
FBA: Asymmetric Rotor
0+0-0+
0-
• CH2OH rotor results in a 2-fold barrier
• Rotor axis is mainly along a-axis
• µa and µb-type transitions• ΔE between 0+ and 0- is small• µb-type transitions are
Coriolis interactions between levels
a
b
FBA ConstantsFBA LIF1 Benzyl Alcohol2
A 0+ (MHz) 4628.9(20) 4758.986(1)B 0+ (MHz) 928.5(10) 1475.398(1)C 0+ (MHz) 803.1(6) 1193.4018(5)A 0- (MHz) 4628.3(15) 4759.133(1)B 0- (MHz) 928.9(10) 1475.409(1)C 0- (MHz) 803.8(10) 1193.3769(5)Fab (MHz) 222.021(8)
Fbc (kHz) 57.418(1)
ΔE (MHz) 492.816(2)
1Nikolaev, A. E, In Preparation2Utzat, K. A.; Bohn, R. K.; Montgomery, J. A.; Michels, H. H.; Caminati, W. The Journal of Physical Chemistry A.
Barrier Problems
• Challenging to measure High Barriers > 500 cm-1
– o-toluidine ≈ 700 cm-1
– JB 95, SPCAT, XIAM• Challenging to simulate Low Barriers– m-toluidine = 4.2 cm-1
– Free rotor limit• Challenging to fit Asymmetric Rotor– FBA: µb and µc >> µa
– Coriolis terms have large effect on µb/µc frequencies
Acknowledgements
Pratt Group: Pate Group:
Dr. David Pratt Dr. Brooks PateJustin Young Justin NeillA.J. Fleisher Matt MucklePhil Morgan Daniel ZaleskiJessica Thomas Amanda SteberCasey ClementsPatrick WalshDr. Vanessa Vaquero
o-Toluidine ConstantsExperimental LIF1
MP2/6-31G+g(d) A Band E Band A Band E Band
A (MHz) 3230.29(1) 3230.35(2) 3230.9(1) 3228.5(1) 3227.85B (MHz) 2188.807(1) 2188.827(2) 2189.0(1) 2189.1(1) 2178.171C (MHz) 1316.940(3) 1316.943(5) 1316.8(1) 1316.9(1) 1313.306χaa (MHz) 2.007(7) 2.02(1)χbb (MHz) 2.05(1) 2.04(2)χcc (MHz) -4.06(1) -4.07(2)DJ (kHz) 0.35(8) 0.5(1)
DJK (kHz) -1.4(3) -2.0(5)DK (kHz) -4(4) -4(7)dJ (kHz) 0.17(5) 0.26 (7)dK(kHz) -0.4(6) 0.5(9)
ΔI (amu Å2) -3.590 -3.586 -3.51 -3.65 -3.768
Lines 52 53
1Morgan, P. J.; Alvarez-Valtierra, L.; Pratt, D. W. The Journal of Physical Chemistry A 2009, 113, 13221-13226.
m-Toluidine ConstantsExperimental LIF1
MP2/6-31G**A Band E Band A Band E Band
A (MHz) 3700.847(4) 3701.3(1) 3700.2(1) 3637.741 B (MHz) 1795.884(4) 1795.9(1) 1795.4(1) 1796.290 C (MHz) 1210.344(4) 1210.4(1) 1210.3(1) 1211.494χaa (MHz) 2.18 (5)χbb (MHz) 2.05(5)χcc (MHz) -4.23(5)DJ (kHz) 0.12(5)
DJK (kHz) -0.6(1)DK (kHz) 1.2(5)dJ (kHz) 0.03(2)dK(kHz) 0.06(40)
ΔI (amu Å2) -0.40 -0.414 -0.508
Lines 60
1Morgan, P. J.; Alvarez-Valtierra, L.; Pratt, D. W. The Journal of Physical Chemistry A 2009, 113, 13221-13226.