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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/
http://cartwright.chem.ox.ac.uk/tlab/605/html/introduction01.htmhttp://cartwright.chem.ox.ac.uk/tlab/605/html/introduction01.htmhttp://cartwright.chem.ox.ac.uk/tlab/605/html/introduction01.htmhttp://www.spectroscopynow.com/raman?tzcheck=1http://www.spectroscopynow.com/raman?tzcheck=1http://www.wurm.info/http://www.wurm.info/http://rruff.info/http://rruff.info/http://www.horiba.com/de/scientific/products/raman-spectroscopy/http://www.horiba.com/de/scientific/products/raman-spectroscopy/http://www.horiba.com/de/scientific/products/raman-spectroscopy/http://www.horiba.com/de/scientific/products/raman-spectroscopy/http://nsdl.niscair.res.in/bitstream/123456789/801/1/http://nsdl.niscair.res.in/bitstream/123456789/801/1/http://www.azom.com/article.aspx?ArticleID=10089http://www.azom.com/article.aspx?ArticleID=10089http://www.gia.edu/Recommended