Ramanova spektroskopija

Igor Lukacevic, Dept. Of Physics, UJJS

Predavanje 9 Atomska fizika i spektroskopija

Sadrzaj

Uvod

Princip rada

Osobine Ramanove spektroskopije

Instrumentacija

Primjene

Ramanova spektroskopija – uvod

C. V. Raman (1888 – 1970)

• Nobelova nagrada 1930.

• Journey into Light: Life

and Science of C. V.

Raman, G.

Venkataraman, 1988.

Ramanova spektroskopija – uvod

Ramanovo rasprsenje ili Ramanov efekt

Neelasticno rasprsenje fotona.

Ramanova spektroskopija – uvod

Osnovne osobine

Dotice se rovibracijske strukture tvari

Uzorak u plinovitom, tekucem ili krutom stanju

Izvor zracenja – laser

Ne mijesati s fluorescencijom

Ramanova spektroskopija – princip

Ramanova spektroskopija – princip

Ram

an

ov p

om

ak

∆𝜔

𝑐𝑚−1

=1 λ0−

1 λ1

Stokesov pomak:

𝐸𝑓 > 𝐸𝑖, 𝜔𝑜𝑢𝑡 < 𝜔𝑖𝑛

Rayleighevo rasprsenje: 𝐸𝑓 = 𝐸𝑖,

𝜔𝑜𝑢𝑡 = 𝜔𝑖𝑛

Anit-Stokesov pomak: 𝐸𝑓 < 𝐸𝑖, 𝜔𝑜𝑢𝑡 > 𝜔𝑖𝑛

Spectrum of CCl4, using an Ar+

laser at 488 nm

Ramanova spektroskopija – princip

The oscillating electric field of the excitation light.

The induced dipole moment from this oscillating field.

The molecular polarizability changes with bond length.

The bond length oscillates at vibrational frequency.

Hence the polarizability oscillates at same frequency.

Substitute.

Remember trig identity.

Induced dipole has Rayleigh,

Stokes, and anti-Stokes

components.

E E0 cosext

induced E E0 cos ex t

0 r req d

dr

r req rmax cosvibt

0 d

dr

rmax cosvibt

induced 0 d

dr

rmax cos vibt

E0 cosex t 0E0 cos ex t

E0rmaxd

dr

cos ex t cosvibt

cosx cosy 1

2cos x y cos x y

induced 0E0 cosex t

E0rmax

2

d

dr

cos ex vib t cos ex vib t

Ramanova spektroskopija – princip

Ramanova spektroskopija – princip

Molekularna polarizabilnost

Ramanova spektroskopija – princip

Molekularna polarizabilnost

𝑟~1

𝜖

Spektar PETN

eksploziva (D.N.

Batchelder, Univ. of

Leeds)

Ramanova spektroskopija – osobine

Nedestruktivna / neinvazivna

metoda

Ne ovisi o temperaturi/tl

aku

ν ≥ 100 𝑐𝑚−1 Jednostavna mikroskopija

Jednostavna ili nikakva priprema

uzorka (voda odlicno

otapalo za Raman i ne rasprsuje se na plastici ili

staklu)

Prednosti Ramanove spektroskopije

Ramanova spektroskopija – osobine

Ramanova spektroskopija – osobine

Ramanova spektroskopija – osobine

Spektar antracena

A: Ar+ laser (514.5 nm)

B: Nd:YAG laser (1064 nm)

𝐼~1

λ4 →

zelimo krace λ

Fluorescencija → zelimo duze λ

• Rayleigh = 105 – 106 SS ili ASS

• ψ𝑣𝑖𝑟𝑡 ≈ ψ𝑟𝑒𝑎𝑙 → 𝑃𝑔𝑠→𝑒𝑥𝑐 ≈ 1

• 𝐼𝑟𝑒𝑠 = 102 − 106 𝐼𝑟𝑎𝑚𝑎𝑛

• c ≥ 10-8 M

• kromofor

Ramanova spektroskopija – osobine

Rezonantni Ramanov ucinak

Ramanova spektroskopija – osobine

• Surface-enhanced Raman spectroscopy

• Resonance Raman spectroscopy

• Surface-enhanced resonance Raman spectroscopy (SERRS)

• Angle-resolved Raman spectroscopy

• Hyper Raman

• Spontaneous Raman spectroscopy (SRS)

• Optical tweezers Raman spectroscopy (OTRS)

• Stimulated Raman spectroscopy

• Spatially offset Raman spectroscopy (SORS)

• Coherent anti-Stokes Raman spectroscopy (CARS)

• Raman optical activity

• Transmission Raman

• Inverse Raman spectroscopy.

• Tip-enhanced Raman spectroscopy (TERS)

• Surface plasmon polaritons enhanced Raman scattering (SPPERS)

Instrumentacija

• Slab I → treba jak intenzitet

• Monokromatski izvor → jednostavniji spektar

• Monokromatski izvor → niska snaga

Lampe

•Ar+ Ion: 488.0 and 514.5 nm

•Kr+ Ion: 530.9 and 647.1 nm

•He:Ne: 632.8 nm

•Diode Lasers: 782 and 830 nm

•Nd: YAG: 1064 (532 when doubled) nm

Laseri

500 mW Ar ion laser – eBay $1000

Tipicne snage izvora

Ion lasers, 40 W cw

He:Ne, 10 W cw

YAG (Yttrium aluminium garnet – Y3Al5O12), 1 J/10 ns pulse (100 MW average pulse)

Poboljsani detektori – potrebna manja snaga

Diode laser, 25 mW

Ar+, 5 mW

Instrumentacija

SSD, SDD, SPD, PIN, CCD

• laser (NIR ili Vis) +

interferometar

• array detektori

Instrumentacija

FT Raman

Multichannel Raman Spectroscopy

Instrument of Hans Hallen in Phyiscs Dept. at North Carolina State.

KTiOPO4 + Rb

NSOM Raman Imaging

A near-field scanning microscope was used and the Raman signal was

used to key the substrate response.

Chemical Mapping

• Focus laser to small spot.

• Tune spectrometer to particular Raman transition peak.

• Raster scan the sample under the laser beam, record intensity changes. Resultant map correlates with

substance.

• Acquire an entire spectrum at every point, then choose the feature

with which to key the image.

Motorized stage from

Renishaw for chemical

mapping.

This is a drug tablet.

The yellow

corresponds to the

active ingredient.

Particles are in the

10’s of µm range.

Chemical Imaging

• Now defocus the laser (not a small spot, but rather “baths” the sample in laser radiation).

• Pass the emitted radiation through a narrow bandpass filter, adjusted to a particular

wavelength, chosen to be a certain Raman band.

• Focus this light on the CCD camera. Bright regions correspond to locations of substance giving

rise to Raman signal.

Mixture of cocaine and sugar. Bright spots are cocaine.

Primjena u restauraciji

• Ovo je freska iz 12. st. iz crkve u Italiji, koju je

trebalo restaurirati

• Koje boje upotrijebiti?

• Raman analiza pomoću Ramanove spektroskopije

identificira boje i pigmente koji su prisutni u originalu,

dozvoljavajući ispravan izbor materijala za čišćenje i

ponovno bojanje nakon toga, kako bi se vratilo

originalno stanje

Applications - Paint Chips

Forensic analysis of paint chips in vehicle accidents. Often

multiple layers. Can analyze with IR by stripping successive

layers. Image edge with microRaman.

• Layers 1 and 3 turned out to be rutile phase TiO2 - a white

paint.

• Layer 2 was a goethite, a red pigment and corrosion inhibitor.

• Layer 4 was molybdate orange, a common red paint in the 70’s

in North America and still used in the U.K. today.

• Layer 5 was a silicate based paint. Data arising from a case

investigated by LAPD.

Applications - Gem Forgery

GE POL (1999) →

brown type IIa diamonds = naturally clear diamonds

Applications - Gem Forgery

GE POL (1999) →

brown type IIa diamonds = naturally clear diamonds

Naturally clear diamond Originally brown diamond

Applications - Bullet Proof Glass

Identify poly(carbonate) from poly(methylmethacrylate).

Both used for shatter-proof glass

Applications - Sunscreen Formulations

Here are the spectra of 5 common

sunscreen ingredients. Raman is able to

determine from a spectrum on the arm

the nature of the sunscreen being used.

A: ODPABA (octyl N,N-dimethyl-p-

aminobenzoic acid)

B: OMC (octyl p-methoxycinnamate)

C: BZ3 (oxybenzone)

D: OCS (octyl salicylate)

E: DBM (dibenzoylmethane)

G. R. Luppnow et al.,

J. Raman. Spec. 34,

743 (2003).

Literatura

1. http://cartwright.chem.ox.ac.uk/tlab/605/html/introduction01.htm

2. http://www.spectroscopynow.com/raman?tzcheck=1

3. http://www.wurm.info/

4. http://rruff.info/

5. http://www.horiba.com/de/scientific/products/raman-spectroscopy/

6. http://nsdl.niscair.res.in/bitstream/123456789/801/1/

7. http://www.azom.com/article.aspx?ArticleID=10089

8. http://www.gia.edu/