Rotational and Vibrational Spectroscopy pdf

1
Lecture Date: January 30
th
, 2008
Rotational and Vibrational
Spectroscopy
Vibrational and Rotational Spectroscopy
 Core techniques:
– Infrared (IR) spectroscopy
– Raman spectroscopy
– Microwave spectroscopy
2
The Electromagnetic Spectrum
 The basic!
 Microwave
 Infrared (IR)
The History of Infrared and Raman Spectroscopy
 Infrared (IR) Spectroscopy:
– First real IR spectra measured by Abney and Festing in 1880’s
– Technique made into a routine analytical method between 1903-
1940 (especially by Coblentz at the US NBS)
– IR spectroscopy through most of the 20
th
century is done with
dispersive (grating) instruments, i.e. monochromators
– Fourier Transform (FT) IR instruments become common in the
1980’s, led to a great increase in sensitivity and resolution
 Raman Spectroscopy:
– In 1928, C. V. Raman discovers that small changes occur the
frequency of a small portion of the light scattered by molecules.
The changes reflect the vibrational properties of the molecule

– In the 1970’s, lasers made Raman much more practical. Near-
IR lasers (1990’s) allowed for avoidance of fluorescence in
many samples.
W. Abney, E. R. Festing, Phil. Trans. Roy. Soc. London, 1882, 172, 887-918.
3
Infrared Spectral Regions
 IR regions are traditionally sub-divided as follows:
Region Wavelength
(), m
Wavenumber
(), cm
-1
Frequency
(), Hz
Near 0.78 to 2.5 12800 to 4000 3.8 x 10
14
to
1.2 x 10
14
Mid 2.5 to 50 4000 to 200 1.2 x 10
14
to
6.0 x 10
12
Far 50 to 1000 200 to 10 6.0 x 10
12
to
3.0 x 10
11
After Table 16-1 of Skoog, et al. (Chapter 16)

What is a Wavenumber?
 Wavenumbers (denoted cm
-1
) are a measure of frequency
– For an easy way to remember, think “waves per centimeter”
 Relationship of wavenumbers to the usual frequency and
wavelength scales:
Image from www.asu.edu


10000
1


cm
 Converting
wavelength () to
wavenumbers:
4
Rotational and Vibrational Spectroscopy: Theory
 Overview:
– Separation of vibrational and rotational contributions to energy is
commonplace and is acceptable
– Separation of electronic and rovibrational interactions
 Basic theoretical approaches:
– Harmonic oscillator for vibration
– Rigid rotor for rotation
 Terminology:
– Reduced mass (a.k.a. effective mass):
See E. B. Wilson, Jr., J. C. Decius, and P. C. Cross, “Molecular Vibrations”, Dover, 1955.

21
21
mm
mm



Rotational Spectroscopy: Theory
 Rotational energy levels can be
described as follows:
R. Woods and G. Henderson, “FTIR Rotational Spectroscopy”, J. Chem. Educ., 64, 921-924 (1987)
DJBJJ
3
)1()1()( 

crhB
2
0
2
8/


23
/4
c
BD


Where:
c is the speed of light

k is the Hooke’s law force constant
r
0
is the vibrationally-averaged bond length
The rotational constant:
The centrifugal distortion coefficient:
u
k
c
c


2
1

Example for HCl:
B
0
= 10.4398 cm
-1
D
0
= 0.0005319 cm
-1
r
0
= 1.2887 Å
 is the reduced mass
h is Planck’s constant


0
= 2990.946 cm
-1
(from IR)
k = 5.12436 x 10
5
dyne/cm
-1
For J = 0, 1, 2, 3…
5
Vibrational Spectroscopy: Theory
 Harmonic oscillator – based on the classical “spring”


m
hvE

2
1


m
is the natural frequency of the oscillator (a.k.a. the fundamental vibrational wavenumber)
k is the Hooke’s law force constant (now for the chemical bond)
u
k
m


2

1

v is the vibrational quantum number
h is Planck’s constant
 Since v must be a whole number (see Ex. 16-1, pg. 386):
 The potential energy function is:
2
2
1
)()(
eHO
rrkrE 
Note – all E are
potential energies (V)!
or
22
2
1
)()2()(
emHO
rrcrE 



kh
hE
m
2




k
12
103.5


and
(wavenumbers)
r is the distance (bond distance)
r
e
is the equilibrium distance
Vibrational Spectroscopy: Theory
 Potential energy of a harmonic oscillator:
Figure from Skoog et al.
6
Anharmonic Corrections
 Anharmonic motion: when the restoring force is not
proportional to the displacement.
– More accurately given by the Morse potential function than by the
harmonic oscillator equation.
– Primarily caused by Coulombic (electrostatic) repulsion as atoms
approach
 Effects: at higher quantum numbers, E gets smaller, and
the ( = +/-1) selection rule can be broken
– Double ( = +/-2), triple ( = +/-3), and higher order transitions
can occur, leading to overtone bands at higher frequencies (NIR)
2
)(
)1()(

e
rra
eMorse
ehcDrE


D
e
is the dissociation energy
e
m
hcD
c
a
2
)2(
2


Vibrational Coupling
 Vibrations in a molecule may couple – changing each
other’s frequency.
– In stretching vibrations, the strongest coupling occurs between
vibrational groups sharing an atom
– In bending vibrations, the strongest coupling occurs between
groups sharing a common bond
– Coupling between stretching and bending modes can occur when
the stretching bond is part of the bending atom sequence.
– Interactions are strongest when the vibrations have similar
frequencies (energies)

– Strong coupling can only occur between vibrations with the same
symmetry (i.e. between two carbonyl vibrations)
7
Vibrational Modes and IR Absorption
 Number of modes:
– Linear: 3n – 5 modes
– Non-linear: 3n – 6 modes
 Types of vibrations:
– Stretching
– Bending
 Examples:
– CO
2
has 3 x 3 – 5 = 4 normal
modes
Symmetric
No change in dipole
IR-inactive
Asymmetric
Change in dipole
IR-active
Scissoring
Change in dipole
IR-active
 IR-active modes require dipole changes during rotations
and vibrations!
Vibrational Modes: Examples
 IR-activity requires
dipole changes
during vibrations!

 For example, this
is Problem 16-3
from Skoog:
Inactive
Active
Active
Active
Inactive
Inactive
Active
8
IR Spectra: Formaldehyde
 Certain types of vibrations have distinct IR frequencies – hence the
chemical usefulness of the spectra
 The gas-phase IR spectrum of formaldehyde:
Formaldehyde spectrum from: />Results generated using B3LYP//6-31G(d) in Gaussian 03W.
 Tables and simulation results can help assign the vibrations!
(wavenumbers, cm
-1
)
Rayleigh and Raman Scattering
 Only objects whose dimension is ~1-1.5  will scatter EM
radiation.
 Rayleigh scattering:
– occurs when incident EM radiation induces an oscillating dipole in
a molecule, which is re-radiated at the same frequency
 Raman scattering:
– occurs when monochromatic light is scattered by a molecule, and
the scattered light has been weakly modulated by the
characteristic frequencies of the molecule

 Raman spectroscopy measures the difference between
the wavelengths of the incident radiation and the
scattered radiation.
9
The Raman Effect
 Polarization changes
are necessary to form
the virtual state and
hence the Raman
effect
 This figure depicts
“normal” (spontaneous)
Raman effects
H. A. Strobel and W. R. Heineman, Chemical Instrumentation: A Systematic Approach, 3
rd
Ed. Wiley: 1989.
hv
1
Scattering timescale ~10
-14
sec
(fluorescence ~10
-8
sec)
Virtual state
Virtual state
hv
1
Ground state
(vibrational)

 The incident radiation excites “virtual states” (distorted
or polarized states) that persist for the short timescale of
the scattering process.
Excited state
(vibrational)
hv
1
– hv
2
Stokes line
hv
1
– hv
2
Anti-Stokes line
More on Raman Processes
 The Raman process: inelastic scattering of a photon
when it is incident on the electrons in a molecule
– When inelastically-scattered, the photon loses some of its energy
to the molecule (Stokes process). It can then be experimentally
detected as a lower-energy scattered photon
– The photon can also gain energy from the molecule (anti-Stokes
process)
 Raman selection rules are based on the polarizability of
the molecule
 Polarizability: the “deformability” of a bond or a molecule
in response to an applied electric field. Closely related to
the concept of “hardness” in acid/base chemistry.
P. W. Atkins and R. S. Friedman, Molecular Quantum Mechanics, 3
rd

Ed. Oxford: 1997.
10
More on Raman Processes
 Consider the time variation of the dipole moment induced
by incident radiation (an EM field):
)()()( ttt




P. W. Atkins and R. S. Friedman, Molecular Quantum Mechanics, 3
rd
Ed. Oxford: 1997.
EM fieldInduced dipole moment
 Expanding this product yields:


tttt )cos()cos(cos)(
intint0
4
1
0















Rayleigh line
Anti-Stokes line Stokes line
polarizability
 If the incident radiation has frequency  and the
polarizability of the molecule changes between 
min
and

max
at a frequency 
int
as a result of this rotation/vibration:


ttt






coscos)(
0int
2

1



mean polarizability
 = 
max
- 
min
The Raman Spectrum of CCl
4
Figure is redrawn from D. P. Strommen and K. Nakamoto, Amer. Lab., 1981,43 (10), 72.
Observed in
“typical”
Raman
experiments

0
= 20492 cm
-1

0
= 488.0 nm
Anti-Stokes lines
(inelastic scattering)
-218
Raman shift cm
-1

0

= (
s
- 
0
)
-200
Stokes lines
(inelastic scattering)
-400400 200
218
314
-314
-459
459
0
Rayleigh line
(elastic scattering)
11
Raman-Active Vibrational Modes
 Modes that are more polarizable are more Raman-active
 Examples:
– N
2
(dinitrogen) symmetric stretch
 cause no change in dipole (IR-inactive)
 cause a change in the polarizability of the bond – as the bond gets
longer it is more easily deformed (Raman-active)
– CO
2
asymmetric stretch

 cause a change in dipole (IR-active)
 Polarizability change of one C=O bond lengthening is cancelled by
the shortening of the other – no net polarizability (Raman-inactive)
 Some modes may be both IR and Raman-active, others
may be one or the other!
The Raman Depolarization Ratio
 Raman spectra are excited by linearly polarized radiation
(laser).
 The scattered radiation is polarized differently depending
on the active vibration.
 Using a polarizer to capture the two components leads to
the depolarization ratio p:



I
I
p
 The depolarization ratio p can be useful in interpreting the
actual vibration responsible for a Raman signal.
12
Instrumentation for Vibrational Spectroscopy
 Absorption vs. Emission for IR spectroscopy:
– Emission is seldom used for chemical analysis
– The sample must be heated to a temperature much greater than its
surroundings (destroying molecules)
– IR emission is widely used in astronomy and in space applications.
 Two IR Absorption methods:
– Dispersive methods: Scanning of wavelengths using a grating
(common examples are double-beam, like a spectrometer

discussed in the optical electronic spectroscopy lecture).
– Fourier-transform methods: based on interferometry, a method of
interfering and modulating IR radiation to encode it as a function
of its frequency.
Radiation
Source
Sample
Wavelength
Selector
Detector
(transducer)
Radiation
Source
Interferometer Sample
Detector
(transducer)
Why Build Instruments for Fourier Transform Work?
 Advantages:
– The Jacqinot (throughput) advantage: FT instruments have
few slits, or other sources of beam attenuation
– Resolution/wavelength accuracy (Connes advantage):
achieved by a colinear laser of known frequency
– Fellgett (multiplex) advantage: all frequencies detected at
once, signal averaging
 These advantages are critical for IR spectroscopy
 The need for FT instruments is rooted in the detector
– There are no transducers that can acquire time-varying signals
in the 10
12
to 10

15
Hz range – they are not fast enough!
 Why are FT instruments not used in UV-Vis?
– The multiplex disadvantage (shot noise) adversely affects
signal averaging – it is better to multiplex with array detectors
(such as the CCD in ICP-OES)
– In some cases, technical challenges to building interferometers
with tiny mirror movements
13
Inteferometers for FT-IR and FT-Raman
 The Michelson
interferometer, the
product of a famous
physics experiment:
 Produces
interference
patterns from
monochromatic
and white light
Figures from Wikipedia.org
Inteferometers
 For monochromatic
radiation, the
interferogram looks like
a cosine curve
 For polychromatic
radiation, each
frequency is encoded
with a much slower
amplitude modulation

 The relationship
between frequencies:
 Example: mirror rate = 0.3 cm/s modulates 1000 cm
-1
light at 600 Hz
 Example: mirror rate = 0.2 cm/s modulates 700 nm light at 5700 Hz

c
v
f
M
2

Where:
 is the frequency of the radiation
c is the speed of light in cm/s
v
m
is the mirror velocity in cm/s
14
The Basics of the Fourier Transform
 The conversion from time- to frequency domain:
50 100 150 200 250
-1
-0.5
0.5
1
50
100
150

200
250
0.5
1
1.5
2
FT
50 100 150 200 250
-1.5
-1
-0.5
0.5
1
1.5
2
50
100
150
200
250
0.5
1
1.5
2
2.5






1
0
/2
1
N
k
Nikn
kn
ed
N
f




b
a
dtftKg

)(),()(
1
)texp(),( iωtK



Continuous:
Discrete:
FT
FTIR Spectrometer Design
Michelson

Interferometer
IR Source
Sample
Moving MirrorFixed Mirror
Beamsplitter
Detector
Interferogram
Fourier Transform - IR Spectrum
 It is possible to build a detector that detects multiple
frequencies for some EM radiation (ex. ICP-OES with CCD,
UV-Vis DAD)
 FTIR spectrometers are designed around the Michelson
interferometer, which modulates each IR individual
frequency with an additional unique frequency:
15
IR Sampling Methods: Absorbance Methods
 Salt plates (NaCl): for liquids (a drop) and small amounts of solids.
Sample is held between two plates or is squeezed onto a single plate.
 KBr/CsI pellet: a dilute (~1%) amount of sample in the halide matrix
is pressed at >10000 psi to form a transparent disk.
– Disadvantages: dilution required, can cause changes in sample
 Mulls: Solid dispersion of sample in a heavy oil (Nujol)
– Disadvantages: big interferences
 Cells: For liquids or dissolved samples. Includes internal reflectance
cells (CIRCLE cells)
 Photoacoustic (discussed later)
IR Sampling Methods: Reflectance Methods
 Specular reflection: direct
reflection off of a flat surface.
– Grazing angles

 Attenuated total reflection
(ATR): Beam passed through
an IR-transparent material with
a high refractive index, causing
internal reflections. Depth is
~2 um (several wavelengths)
 Diffuse reflection (DRIFTS): a
technique that collects IR
radiation scattered off of fine
particles and powders. Used
for both surface and bulk
studies.
Figures from />ATR
DRIFTS
16
IR Sources
 Nernst glower: a rod or cylinder made from several grams
of rare earth oxides, heated to 1200-2200K by an electric
current.
 Globar: similar to the Nernst glower but made from silicon
carbide, electrically heated. Better performance at lower
frequencies.
 Incandescent Wires: nichrome or rhodium, low intensity
 Mercury Arc: high-pressure mercury vapor tube, electric
arc forms a plasma. Used for far-IR
 Tungsten filament: used for near-IR
 CO
2
Lasers (line source): high-intensity, tunable, used for
quantitation of specific analytes.

IR Detectors
 Thermal transducers
– Response depends upon heating effects of IR radiation
(temperature change is measured)
 Slow response times, typically used for dispersive instruments or
special applications
 Pyroelectric transducers
– Pyroelectric: insulators (dielectrics) which retain a strong electric
polarization after removal of an electric field, while they stay
below their Curie temperature.
– DTGS (deuterated triglycine sulfate): Curie point ~47°C
 Fast response time, useful for interferometry (FTIR)
 Photoconducting transducers
– Photoconductor: absorption of radiation decreases electrical
resistance. Cooled to LN
2
temperatures (77K) to reduce thermal
noise.
– Mid-IR: Mercury cadmium telluride (MCT)
– Near-IR: Lead sulfide (NIR)
17
Raman Spectrometers
 The basic design dispersive Raman scattering system:
 Special considerations:
– Sources: lasers are generally the only source strong enough to
scatter lots of light and lead to detectable Raman scattering
– Avoiding fluorescence: He-Cd (441.6 nm), Ar ion (488.0 nm,
514.5 nm), He-Ne (632.8), Diode (782 or 830), Nd/YAG (1064)
Sample
Wavelength

Selector
Detector
(photoelectric transducer)
Radiation
source
(90° angle)
Modern Raman Spectrometers
 FT-Raman spectrometers – also make use of Michelson
interferometers
– Use IR (1 m) lasers, almost no problem with fluorescence for
organic molecules
– Have many of the same advantages of FT-IR over dispersive
– But, there is much debate about the role of “shot noise” and
whether signal averaging is really effective
 CCD-Raman spectrometers – dispersive spectrometers
that use a CCD detector (like the ICP-OES system
described in the Optical Electronic lecture)
– Raman is detected at optical frequencies!
– Generally more sensitive, used for microscopy
– Usually more susceptible to fluorescence, also more complex
 Detectors - GaAs photomultiplier tubes, diode arrays, in
addition to the above.
18
More on Raman
 Raman can be used to study aqueous-phase samples
– IR is normally obscured by H
2
O modes, these happen to be less
intense in Raman
– However, the water can absorb the scattered Raman light and

will damp the spectrum, and lower its sensitivity
 Raman has several problems:
– Susceptible to fluorescence, choice of laser important
– When used to analyze samples at temperatures greater than
250C, suffers from black-body radiation interference (so does
IR)
– When applied to darkly-colored samples (e.g. black), the Raman
laser will heat the sample, can cause decomposition and/or
more black-body radiation
Applications of Raman Spectroscopy
 Biochemistry: water is not strongly detected in Raman
experiments, so aqueous systems can be studied.
Sensitive to e.g. protein conformation.
 Inorganic chemistry: also often aqueous systems.
Raman also can study lower wavenumbers without
interferences.
 Other unique examples:
– Resonance Raman spectroscopy: strong enhancement (10
2
–
10
6
times) of Raman lines by using an excitation frequency close
to an electronic transition (Can detect umol or nmol of analytes).
– Surface-enhanced Raman (SERS): an enhancement obtained
for samples adsorbed on colloidal metal particles.
– Coherent anti-Stokes Raman (CARS): a non-linear technique
using two lasers to observe third-order Raman scattering – used
for studies of gaseous systems like flames since it avoids both
fluorescence and luminescence issues.

19
Applications of Raman Spectroscopy
 Raman in catalysis research (see C&E News, Oct. 13,
2006, pg. 59):
– Useful for the study of zeolite interiors
– Fluorescence can be a problem, but one approach is to use UV
light (257 nm) which avoids it just like switching to the IR (but at
the risk of decomposition) – See work from the Stair group at
Northwestern
– For uses of SERS: Catal. Commun 3 547 (2002).
 Raman microscopy: offers sub-micrometer lateral
resolution combined with depth-profiling (when combined
with confocal microscopy)
Comparison of IR and Raman Spectroscopy
 Advantages of Raman over IR:
– Avoids many interferences from solvents, cells and sample
preparation methods
– Better selectivity, peaks tend to be narrow
– Depolarization studies possible, enhanced effects in some cases
– Can detect IR-inactive vibrational modes
 Advantages of IR over Raman:
– Raman can suffer from laser-induced fluorescence and
degradation
– Raman lines are weaker, the Rayleigh line is also present
– Raman instruments are generally more costly
– Spectra are spread over many um in the IR but are compressed
into several nm (20-50 nm) in the Raman
 Final conclusion – they are complementary techniques!
20
Interpretation of IR and Raman Spectra

 General Features:
– Stretching frequencies are greater (higher wavenumbers) than
corresponding bending frequencies
 It is easier to bend a bond than to stretch it
– Bonds to hydrogen have higher stretching frequencies than those
to heavier atoms.
 Hydrogen is a much lighter element
– Triple bonds have higher stretching frequencies than double
bonds, which have higher frequencies than single bonds
 Strong IR bands often correspond to weak Raman bands
and vice-versa
Interpretation of IR and Raman Spectra
Characteristic Vibrational Frequencies for Common Functional Groups
Frequency (cm
-1
) Functional Group Comments
3200-3500 alcohols (O-H)
amine, amide (N-H)
alkynes (CC-H)
Broad
Variable
Sharp
3000 alkane (C-C-H)
alkene (C=C-H)
2100-2300 alkyne (CC-H)
nitrile (CN-H)
1690-1760 carbonyl (C=O) ketones, aldehydes,
acids
1660 alkene (C=C)
imine (C=N)

amide (C=O)
Conjugation lowers
amide frequency
1500-1570
1300-1370
nitro (NO
2
)
1050-1300 alcohols, ethers, esters,
acids (C-O)
See also Table 17-2 of Skoog, et al.
More detailed lists are widely available. See R. M. Silverstein and F. X. Webster, “Spectrometric Identification of Organic Compounds”, 6
th
Ed., Wiley, 1998.
21
IR and Raman Spectra of an Organic Compound
The IR and Raman spectra of
flufenamic acid (an analgesic/anti-
inflammatory drug):
CF
3
O OH
FT-IR Flufenamic acid Aldrich as recd
0.05
0.10
0.15
0.20
0.25
0.30
Abs

FT-Raman Flufenamic acid Aldrich as recd
0
10
20
30
40
50
60
Int
500 1000 1500 2000 2500 3000 3500
Raman shift (cm-1)
IR and Raman Spectra of an Organic Compound
The IR and Raman spectra of
flufenamic acid (an analgesic/anti-
inflammatory drug):
CF
3
O OH
FT-IR Flufenamic acid Aldrich as recd
0.05
0.10
0.15
0.20
0.25
0.30
Abs
FT-Raman Flufenamic acid Aldrich as recd
0
10
20

30
40
50
60
Int
200 400 600 800 1000 1200 1400 1600
Wavenumbers (cm-1)
Note – materials
usually limit IR
in this region
22
IR and Raman Spectra of an Organic Compound
The IR and Raman spectra of tranilast:
Tranilast Form I FV101031-171A1 FTIR
0.1
0.2
0.3
0.4
0.5
0.6
Abs
Tranilast Form I FV101031-171A1 FT-Raman
100
200
300
400
500
Int
500 1000 1500 2000 2500 3000 3500
Wavenumbers (cm-1)

O
O
N
H
O
OHO
C1
C6C2
C3
C4
C5
C7
N1
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18
H
3
C
H
3
C

O4
O5
O3
O2
O1
IR Frequencies and Hydrogen Bonding Effects
 IR frequencies are sensitive to
hydrogen-bonding strength and
geometry (plots of relationships
between crystallographic distances
and vibrational frequencies):
G. A. Jeffrey, An Introduction to Hydrogen Bonding, Oxford, 1997.
23
Applications of Far IR Spectroscopy
 Far IR is used to study low frequency vibrations, like those between
metals and ligands (for both inorganic and organometallic chemistry).
– Example: Metal halides have stretching and bending vibrations in the
650-100 cm
-1
range.
– Organic solids show “lattice vibrations” in this region
 Can be used to study crystal lattice energies and semiconductor
properties.
 The Far IR region also overlaps rotational bands, but these are
normally not detectable in condensed-phase work
Terahertz Spectroscopy
 A relatively new technique, addresses an unused portion
of the EM spectrum (the “terahertz gap”):
– 50 GHz (0.05 THz) to 3 THz (1.2 cm
-1

to 100 cm
-1
)
 Made possible with recent innovations in instrument
design, accesses a region of crystalline phonon bands
P. F. Taday and D. A. Newnham, Spectroscopy Europe, , www.spectroscopyeurope.com
G. Winnewisser, Vibrational Spectroscopy8 (1995) 241-253
24
Applications of Near IR Spectroscopy
 Near IR – heavily used in process chemistry
 Amenable to quantitative analysis usually in conjunction with
chemometrics (calibration requires many standards to be run)
 While not a qualitative technique, it can serve as a fast and useful
quantitative technique especially using diffuse reflectance
 Accuracy and precision in the ~2% range
 Examples:
– On-line reaction monitoring (food, agriculture, pharmaceuticals)
– Moisture and solvent measurement and monitoring
 Water overtone observed at 1940 nm
– Solid blending and solid-state issues
Near IR Spectroscopy
Figure from www.asdi.com. For more information see:
1. Ellis, J.W. (1928) “Molecular Absorption Spectra of Liquids Below 3 m”, Trans. Faraday Soc. 1928, 25, pp. 888-898.
2. Goddu, R.F and Delker, D.A. (1960) “Spectra-structure correlations for the Near-Infrared region.” Anal. Chem., vol. 32 no. 1, pp. 140-141.
3. Goddu, R.F. (1960) “Near-Infrared Spectrophotometry,” Advan. Anal. Chem. Instr. Vol. 1, pp. 347-424.
4. Kaye, W. (1954) “Near-infrared Spectroscopy; I. Spectral identification and analytical applications,” Spectrochimica Acta,vol. 6, pp. 257-287.
5. Weyer, L. and Lo, S C. (2002) Spectra-Structure Correlations in the Near-infrared, In Handbook of Vibrational Spectroscopy, Vol. 3, Wiley, U.K., pp. 1817-1837.
6. Workman, J. (2000) Handbook of Organic Compounds: NIR, IR, Raman, and UV-Vis Spectra Featuring Polymers and Surfactants, Vol. 1, Academic Press, pp. 77-197.
25
Near IR Spectrum of Acetone

 NIR taken in transmission mode (via a reflective gold plate) on a
Foss NIRsystems spectrometer
 Useful for quick solvent identification
Near IR Spectrum of Water (1
st
Derivative)
 1
st
derivative (and 2
nd
derivative) allows for easier identification of
bands