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)

o-Toluidine

10000 avg500 MHz CP

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

m-Toluidine

10000 avg500 MHz CP

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

4-Fluorobenzyl Alcohol

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.