OSU 06/19/08

Ultrabroadband Rotational Spectroscopy:  Novel Applications of a Shape Sensitive Detector

BRIAN C. DIANPurdue University

Department of Chemistry 560 Oval Dr,

West Lafayette, IN 47907-2084

Chandana KarunatilakaPost-Doc

Amanda ShirarGraduate Student

Giana StorckGraduate Student

Kelly HotoppGraduate Student

Erin Blaze BiddleUndergraduate

Ricky Crawley Jr.Undergraduate

OSU 06/19/08

Why 2D?

• Ground State Applications

– Molecules with many conformers

– Low barrier torsional motion

• Toluene

– Biomolecules

• Excited State Dynamics

– Dynamic Rotational Spectroscopy

• Assigning molecular Eigenstates

• Rotational Spectroscopic Analogs of 2D NMR

• Built upon work from Vogelsanger et. al., CPL (1988) v.144, 2, p. 180.

OSU 06/19/08

18.9 GHzPDRO

12 GHz Oscilloscope

(40 Gs/s)

200W

ArbitraryWaveformGenerator

100 MHz Quartz Oscillator

GHz Chirped Pulse0.1-5 GHz

8-18 GHz

Pulsed SampleNozzle

0.9-10.9 GHz26.9-36.9 GHz

1)

2) Interaction

3)

Free InductionDecay

How Do we Do This? Condensed Circuit Diagram

20 dB

13.0 GHzPDRO

OSU 06/19/08

18.9 GHzPDRO

12 GHz Oscilloscope

(40 Gs/s)

200W

ArbitraryWaveformGenerator

100 MHz Quartz Oscillator

Pulsed SampleNozzle

0.9-10.9 GHz26.9-36.9 GHz

1)

2) Interaction

3)

Free InductionDecay

x4

20 dB

How Do we Do This? Condensed Circuit Diagram

GHz Chirped Pulse1.875-4.625 GHz

7.5-18.5 GHz

OSU 06/19/08

18.9 GHzPDRO

12 GHz Oscilloscope

(40 Gs/s)

200W

ArbitraryWaveformGenerator

100 MHz Quartz Oscillator

Pulsed SampleNozzle

0.9-10.9 GHz26.9-36.9 GHz

1)

2)

3) Detection

Free InductionDecay

x4

20 dB

How Do we Do This? Condensed Circuit Diagram

GHz Chirped Pulse1.875-4.625 GHz

OSU 06/19/08

Asymmetric rotor

~ 20000:1 signal-to-noise across entire Bandwidth

Lines split by nuclear hyperfine of Cl

FWHM Linewidth 65 kHz 20 s gate

b ~ 1.2 Debye

Ground State Spectrum of 1-Chloro-1-FluoroEthylene000-111000-111

OSU 06/19/08

Development of 2-D Rotational Spectroscopy

- Experimental Design (NMR Analogs) Autocorrelation Spectra

- Non-Selective Excitation- Pump all conformers- Probe all conformers- Complex interpretation of time domain spectrum

J=0

J=2

J=1

Frequency DomainEnergy Level Scheme

MW Probe

Excitation Source

Time DomainSelective Excitation

pu

mp

pro

be

1

(Scan)

- Pump/Probe pulses 10-100 nsec long- 1 varied from 2-.1 nsec- Magnitude FT taken in two dimensions

OSU 06/19/08

Time DomainSelective Excitation

pu

mp 1

pro

be

(Scan)

000N=1.5

111

10 ns 10 ns

N=2.5

N=0.5N=1.5

Selection Rules N = 1

Energy Level Scheme

Ground State 2D Rotational Autocorrelation Spectra

A

CB

OSU 06/19/08

Ground State 2D Rotational Autocorrelation Spectra

Time DomainSelective Excitation

pu

mp 1

pro

be

(Scan)

000N=1.5

111

10 ns 10 ns

F=2.5

F=0.5F=1.5

Selection Rules F = 1

Energy Level Scheme

OSU 06/19/08

Ground State Spectrum of 1-chloro-1-flouroethylene

000-111

111-202

202-211

OSU 06/19/08

Data Work Up Issues :

- 20 s x 20 s digitization at 40 Gs/s 1.6x1011 data points (after FT)

- S/N Increases a digitization gets longer: Want to digitize as long as possible (w/in limitations of experimental T2)

- Significantly reduce points in first dimension by taking ‘cuts’ of the spectral region of interest only

- Increases digitization in 2nd Dimension

- Workable solution to < 2 million data points (about what most current desktop applications can handle.)

OSU 06/19/08

Experimental Solution-Experimental Design (NMR Analogs)

- Only consider single “connected” hyperfine peaks across four J levels

- Selective Excitation- Fold Quantum Resonances onto “carrier” pulse

- Digitize at full sampling rate to ‘unwrap’ folded signal- Full broadband results are projected onto a single hyperfine clump

J=000

J=202

J=111

Frequency DomainEnergy Level Scheme

Carrier Frequency

- Pump/Probe pulses 100 nsec long

- 1 100 psec step size

- Magnitude FT taken in two dimensions

J=211

1

(Scan)

Pump Project

F=1.5

F=2.5

F=3.5

F=3.5

OSU 06/19/08

Broadband 2D Spectra

>1.2 million data points represented in graph

4 s digitization at 40 Gs/s along x-axis

1600 ns digitization at 10 Gs/s along y-axis

OSU 06/19/08

Broadband 2D 000111 Spectral Region

OSU 06/19/08

Broadband 2D 202211 Spectral Region

OSU 06/19/08

Conclusions• Full broadband is not quite ready for prime

time.• Experimentally worked around by projecting

on a single carrier frequency.• Theoretically any number of peaks can be

projected onto the carrier as long as they are connected to the carrier.

• Bandwidths of 500MHz (possibly up to 1 GHz) are realizable.

• Good news! Increases in digital memory are occurring rapidly!

OSU 06/19/08

Acknowledgements

Funding:• Purdue University

• Camille and Henry Dreyfus Young Faculty Award

• Chandana Karunatilaka: Post-Doc• Amanda Shirar: Graduate Student• Giana Storck: Graduate Student• Kelly Hotopp: Graduate Student• Erin Blaze Biddle : Undergraduate• Ricky Crawley Jr.: Undergraduate

Students:

OSU 06/19/08

FROG: 1 ns Sinc

Pulse