1. Ramanova spektroskopija
Igor Lukacevic, Dept. Of Physics, UJJS
Predavanje 9
Atomska fizika i spektroskopija

2. Sadrzaj Uvod Princip rada Osobine Ramanove spektroskopije
Instrumentacija
Primjene

3. Ramanova spektroskopija – uvod
C. V. Raman (1888 – 1970)
Nobelova nagrada 1930.
Journey into Light: Life and Science of C. V. Raman, G. Venkataraman, 1988.

4. Ramanova spektroskopija – uvod
Ramanovo rasprsenje ili Ramanov efekt
Neelasticno rasprsenje fotona.

5. Ramanova spektroskopija – uvod
Osnovne osobine
Dotice se rovibracijske strukture tvari
Uzorak u plinovitom, tekucem ili krutom stanju
Izvor zracenja – laser
Ne mijesati s fluorescencijom

6. Ramanova spektroskopija – uvod
Another spectroscopic technique which probes the rovibrational structure of molecules.
Can probe gases, liquids, and solids.
Must use a laser source for excitation.
Resurgence in recent years due to the development of new detectors with improved sensitivity.
Shift back away from FT-Raman to dispersive Raman with multichannel detector systems.

7. Ramanova spektroskopija – princip

8. Ramanova spektroskopija – princip
Ramanov pomak ∆𝜔 𝑐𝑚 −1 = 1 λ 0 − 1 λ 1
Stokesov pomak: 𝐸 𝑓 > 𝐸 𝑖 , 𝜔 𝑜𝑢𝑡 < 𝜔 𝑖𝑛
Rayleighevo rasprsenje: 𝐸 𝑓 = 𝐸 𝑖 , 𝜔 𝑜𝑢𝑡 = 𝜔 𝑖𝑛
Anit-Stokesov pomak: 𝐸 𝑓 < 𝐸 𝑖 , 𝜔 𝑜𝑢𝑡 > 𝜔 𝑖𝑛

9. Ramanova spektroskopija – princip
Spectrum of CCl4, using an Ar+ laser at 488 nm

10. Ramanova spektroskopija – princip
A complete Raman spectrum consists of:
• a Rayleigh scattered peak (high intensity, same wavelength as excitation)
• a series of Stokes-shifted peaks (low intensity, longer wavelength)
• a series of anti-Stokes shifted peaks (still lower intensity, shorter wavelength)
• spectrum independent of excitation wavelength (488, 632.8, or 1064 nm)
Spectrum of CCl4, using an Ar+ laser at 488 nm.

11. 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.

12. Ramanova spektroskopija – princip
Molekularna polarizabilnost

13. Ramanova spektroskopija – princip
Molekularna polarizabilnost
𝑟~ 1 𝜖

14. Ramanova spektroskopija – osobine
Spektar PETN eksploziva (D.N. Batchelder, Univ. of Leeds)

15. Ramanova spektroskopija – osobine
Prednosti Ramanove spektroskopije
Nedestruktivna / neinvazivna metoda
Ne ovisi o temperaturi/tlaku
ν ≥100 𝑐𝑚 −1
Jednostavna mikroskopija
Jednostavna ili nikakva priprema uzorka (voda odlicno otapalo za Raman i ne rasprsuje se na plastici ili staklu)

16. Ramanova spektroskopija – osobine

17. Ramanova spektroskopija – osobine
𝐼~ 1 λ 4 → zelimo krace λ
Fluorescencija → zelimo duze λ
Spektar antracena
A: Ar+ laser (514.5 nm)
B: Nd:YAG laser (1064 nm)

18. Ramanova spektroskopija – osobine
Rezonantni Ramanov ucinak
Rayleigh = 105 – 106 SS ili ASS
ψ 𝑣𝑖𝑟𝑡 ≈ ψ 𝑟𝑒𝑎𝑙 → 𝑃 𝑔𝑠→𝑒𝑥𝑐 ≈1
𝐼 𝑟𝑒𝑠 = 10 2 − 𝐼 𝑟𝑎𝑚𝑎𝑛
c ≥ 10-8 M
kromofor

19. 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)

20. Instrumentacija
Raman intensity is weak and the excitation source must be strong to generate sufficient signal.
Source must be monochromatic so that spectrum is sufficiently uncomplicated.
Intense lamps can work, but when monochromatized, have very little power.
Scattering efficiency increases as n4: the bluer the light, the more the scattering.
The bluer the light, the greater the chance of producing fluorescence.
Lasers are used almost exclusively:
Ar+ Ion: and nm
Kr+ Ion: and nm
He:Ne: nm
Diode Lasers: 782 and 830 nm
Nd: YAG: 1064 (532 when doubled) nm
I just checked. Here is a 500 mW Ar ion laser for sale on eBay for $1000.

21. Instrumentacija 500 mW Ar ion laser – eBay $1000
Lampe
Slab I → treba jak intenzitet
Monokromatski izvor → jednostavniji spektar
Monokromatski izvor → niska snaga
Laseri
Ar+ Ion: and nm
Kr+ Ion: and nm
He:Ne: nm
Diode Lasers: 782 and 830 nm
Nd: YAG: 1064 (532 when doubled) nm
500 mW Ar ion laser – eBay $1000

22. Instrumentacija 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
SSD, SDD, SPD, PIN, CCD

23. Instrumentacija FT Raman laser (NIR ili Vis) + interferometar
array detektori

24. Multichannel Raman Spectroscopy
Instrument of Hans Hallen in Phyiscs Dept. at North Carolina State.

25. NSOM Raman Imaging KTiOPO4 + Rb
A near-field scanning microscope was used and the Raman signal was used to key the substrate response.
KTiOPO4 + Rb

26. 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.
This is a drug tablet. The yellow corresponds to the active ingredient. Particles are in the 10’s of µm range.
Motorized stage from Renishaw for chemical mapping.

27. 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.

28. 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

29. 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.

30. Applications - Gem Forgery
GE POL (1999) →
brown type IIa diamonds = naturally clear diamonds
Original manufacturer engraved “GE POL” on side of diamond to prevent their fraudulent sale. Within the year, evidence of wrong doing was mounting. People were removing the label and then reselling them.

31. Applications - Gem Forgery
GE POL (1999) →
brown type IIa diamonds = naturally clear diamonds
Originally brown diamond
Naturally clear diamond
Original manufacturer engraved “GE POL” on side of diamond to prevent their fraudulent sale. Within the year, evidence of wrong doing was mounting. People were removing the label and then reselling them.

32. Applications - Bullet Proof Glass
Identify poly(carbonate) from poly(methylmethacrylate).
Both used for shatter-proof glass

33. 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).

34. Literatura