Features
 “Anatomy” 
of
Raw Chemical State Spectra

 



Topic #1:  Why do we collect Chemical State Spectra?

Topic #2:  Features of a Raw Chemical State Spectrum

Topic #3:  Two Types of Principle XPS Signals:   Singlet and Doublet

Topic #4:  Which XPS Signals are used to measure Chemical State Spectra? 

Topic #5:  Features of Peak-fitted Chemical State Spectra

Topic #6:  Useful Reference Tables of BEs and FWHMs

 



 

Topic #1 – Why do we collect Chemical State Spectra ?

 

  • A Chemical State Spectrum helps us to decide:
    • If an element is present in one or more chemical states / chemical species / oxidation states
    • The relative percentage of the different chemical states found by peak-fitting
    • If our last experiment produced any changes to the chemical state spectra by comparing before and after spectra
  • Survey Spectra are normally run before and after we collect Chemical State Spectra
    • If chemical state degradation is suspected, then run a repeating series (10-20 spectra) of that same spectrum over 1 hours time.
  • Can Chemical State Spectra of the C (1s) be used to Charge Reference or Charge Correct all High Resolution BEs?
    • Yes and No
    • The C (1s) BE of the hydrocarbon type of carbon found on all materials has commonly been used to correct for charging that occurs when an insulating sample is exposed to a low voltage beam of electrons from an electron flood gun.  This C (1s) BE is defined by the user to occur somewhere between 284.6 eV and 285.2 eV, but there is NO standard or absolute value for the BE of hydrocarbons.  In the literature we can find a range of C (1s) BEs.  Recently, the more common C (1s) BE is 284.8 eV or 285.0 eV. Again, there is no standard.
    • BEs from Conductive or Semi-conductive samples should not and do not need to be charge referenced or charge corrected even though the measured C (1s) BE of the hydrocarbon peak does not appear at 284.8 or 285.0 eV.  The surface of various materials that have non-conductive native oxides and various complex semi-conductors produce a Surface Dipole Moment that causes the hydrocarbon C (1s) BE to shift.  This is a natural phenomenon that needs to be studied.
  • From Chemical State Spectra we can …
    • Determine the thickness of one layer if we the peak-fit includes the pure element as one component
    • Overlay the raw chemical state spectra and find very subtle changes in chemistry of a before and after pair of samples
    • Using advanced software measure thicknesses of several very thin layers
  • Potential Degradation of Surface Chemistry during XPS Analysis due to X-rays, Vacuum, or Electron Flood Gun
    • If chemical state degradation is suspected, then run a repeating series (10-20 spectra) of that same spectrum over 1 hours time.
  • Are High Energy Resolution Spectra the same as Chemical State Spectra? Yes.
  • Core Hole Lifetimes are Measured from Peak FWHMs
    • Core-hole lifetimes are measured in “eV” units for convenience.  These lifetimes are very useful to theoreticians and very advanced measurements.

 



 

Topic #2 – Features of a Raw Chemical State Spectrum

 

Experimental Results from XPS Analyses are plotted on X and Y axes to form a Spectrum

  • X-Axis (horizontal) is the Binding Energy “BE” (eV) of Photo-electrons Analyzed
  • Y-Axis (vertical) is the total number of Photo-electrons Counted (Cts) at each data point (channel)

 

Raw Chemical State Spectrum

 



 

Raw Chemical State Spectrum – X and Y Values, and Axis Labels

 

 



 

Typical Experimental Parameters used to Collect a Chemical State Spectrum

 

 



 

Basic Features of a Raw Chemical State Spectrum

 

 



 

 

Topic #2 – Features of a Raw Chemical State Spectrum

 

(A very simple example)

One (1) single symmetrical peak from a Principle XPS signal.

 

Basic Features of Every
Chemical State Spectrum
Simple Chemical State Spectrum – Element “X”
  • Background intensity, (B)
  • Background noise
  • Background rise
  • Background shape
  • Binding energy, BE, scale, (X axis)
  • Electron counts, cts, scale, (Y axis)
  • Noise in signal, (S)
  • Peak
  • Peak area
  • Peak binding energy, BE
  • Peak full width at half maximum, (FWHM)
  • Peak intensity/height, (S)
  • Peak-shape, % Gaussian, (%G)
  • Peak-shape, % Lorentzian, (%L)
  • Peak-shape, (%G, %L)
  • Peak background shape
  • Signal/Noise ratio, S/N
  • Signal/Background, S/B
  • Routine BE range (spectral window) is often 20-30 eV wide
  • Advanced spectrum analysis often requires a BE range between 50-150 eV to be able to analyze the satellites that exist for complex chemical state materials
  • A chemical state spectrum is also known as a High (Energy) Resolution Spectrum, or a Narrow Scan.
Principle XPS Signal from Oxygen

NOTEs:

  • Element “X” is Oxygen. 
  • Based on well known BE tables, the principle Oxygen signal appears at ~532 eV due to the O (1s) type of photo-electrons.  
  • Because this single peak is symmetrical, this peak probably represents (contains) only one type of Oxygen. 
  • It is possible to add 2 more very small peaks with the same FWHM at the high and low BE ends of this peak, but there are no obvious shoulders that indicate that there might be more than just one single peak. For that reason we would probably use only one “synthetic” peak to fit this raw chemical state spectrum.
  • “1s, 2s, 3s, and 4s” type photo-electrons do not have spin-orbit coupling so they can not appear as doublets.
  • “s” type photo-electrons are “singlets” due to the absence of spin-orbit coupling.
  • A chemical state spectrum is also known as a High (Energy) Resolution Spectrum, or a Narrow Scan.
  • This spectrum is from a Principle (Main) Signal that forms a single peak because this type of photo-electron “1s” can NOT have  spin-orbit coupling.

 

 



 

Features of a Raw Chemical State Spectra  –  Continued

 



 

 

Raw Chemical State Spectrum from Element “Y”

(A more complex example)

 

We see three (3) large peaks and one (1) small peak (total of 4 component-peaks)

 

Features not seen in above example

  • 3 Obvious Large Peaks
  • 1 Small Peak
  • 1 Very small peak (ignored)
  • Shake-up peak (π→π*)
  • This is an insulator so BE scale was adjusted so the hydrocarbon C (1s) peak appears at 285.0 eV
  • The smaller two peaks are due to chemical bonding to different types of oxygen (C-OR, O=C-OR)
  • The main peak is due to C-C and C-H and sp3 type of Carbon
  • The small peak at 292 eV is due to sp2 aromatic carbons that have a pi->pi* electronic state
  • A chemical state spectrum is also known as a High (Energy) Resolution Spectrum, or a Narrow Scan.
  • This spectrum is from a Principle (main) Signal that forms a “singlet” because it is NOT spin-orbit coupled.
NOTEs:
  • This element “Y” is Carbon. 
  • The Principle Carbon Signal appears at ~285 eV BE due to the binding energy of C (1s) type of photo-electrons.
  • The “1s” type of photo-electrons can not display spin-orbit coupling, so this spectrum is less complex.
  • The range of BEs for chemical compounds of Carbon is between 282 to 294 eV due to the electronegativity of the elements that can form chemical bonds to carbon.
  • Carbides appear in the 282-284 eV region.
  • CF2 groups appear in the 290-294 eV region.
  • Carbon bound to Oxygen, Nitrogen, Sulfur and other elements produce C (1s) peaks between 282 and 294 eV.
  • “1s, 2s, 3s, and 4s” type photo-electrons can not have spin-orbit coupling.
  • “s” type photo-electrons are “singlets”.  They can have various sub-peaks, but there is no spin-orbit coupling,
  • Due to differences in electronegativity between different adjacent atoms that are bonded together, the “s” type electrons can form various component peaks as shown here in this C (1s) example. 
  • The O (1s) signal shown as example 1, can produce various component peaks due to those electronegativity differences.

 



 

 

Topic #3:  Two Types of Principle XPS Signals:
Singlet and Doublet

 

Raw Chemical State Spectra often have Spin-Orbit Coupling  Doublets

These Examples shows Principle XPS Signals that are Split into 2 signals due to Spin-Orbit Coupling

 

Peak Shapes and Peak Area Ratios of “s”, “p”, “d”, and “f”  Type XPS Signals

 

“s” type signal

from electrons in “s” orbital
NO spin-orbit splitting
coupling is NOT possible
a “Singlet”
“p” type signals

from electrons in “p” orbitals
Split due to spin-orbit coupling
4:2 peak area ratio
a “Doublet”
d” type signals

from electrons in “d” orbitals
Split due to spin-orbit coupling
6:4 peak area ratio
a “Doublet”
“f” type signals

from electrons in “f” orbitals
Split due to spin-orbit coupling
8:6 peak area ratio
a “Doublet”

 

 



 

Examples of Raw Chemical State Spectra with Spin-Orbit Coupling  

 



Topic #3:

 

Raw Chemical State Spectrum of pure Indium, “In” metal
that has Spin-Orbit Coupling

 

Features

  • Two (2) large peaks
  • In (3d5/2) peak appears at 444 eV
  • In (3d3/2), peak appears at 452 eV
  • The energy difference between these two peaks is 7.5 eV
  • Two (2) small peaks
  • Three (3) very small peaks
  • These small peaks are often called satellites or plasmons
Another simple Chemical State Spectrum but this spectrum has spin-orbit coupled peaks.  Most XPS Signals are spin-orbit coupled.

  • The high energy resolution, chemical state spectrum shown here is from pure Indium (In) metal.  
  • Indium (In) has two large principle peaks that are spin-orbit coupled:   In (3d5/2) and In (3d3/2),   443.8 and 451.3 eV
  • Only the In (3d5/2) is used to check for the presence or absence of difference chemical states of Indium
  • The data-collector needed to analyze the chemical states of Indium for a sample, so he/she programmed the XPS instrument to collect data from 435 eV to 535 eV.
  • To resolve different chemical states that have a small chemical shift difference (~0.5 eV) the data-collector used a large X-ray spot size, a pass energy = 25 eV, with a step size of 0.1 eV, a 100 eV spectral window, and a dwell time of 50 msec.
  • These principle peaks are analyzed when the scientist wants to know what chemical states of Indium exist on/in the surface of a sample. 
  • The two large peaks are due to photoelectrons coming from the In (3d5/2) and In (3d3/2) orbitals of pure Indium.
  • The various small peaks are due to plasmons from pure Indium metal
  • At the base of the two strong peaks, we see sloping asymmetric lines attributed to valence-core electron interactions

In normal size



Topic #3:

Raw Chemical State Spectrum of pure Bismuth, “Bi” metal
that has Spin-Orbit Coupling

 

Features

  • Routine BE range (spectral window) is often 20-30 eV wide
  • Advanced spectrum analysis often requires a BE range between 50-150 eV to be able to analyze the satellites that exist for complex chemical state materials
  • The energy difference between these two peaks is 5.3 eV
  • Two (2) small broad peaks
  • These small peaks are often called satellites or plasmons
  • Bi (4f7/2) peak appears at
    158 eV
  • Bi (4f5/2), peak appears at
    163 eV
A simple Chemical State Spectrum that involves spin-orbit coupled peaks

  • The high energy resolution, chemical state spectrum shown here is from pure Bismuth (Bi) metal.  
  • Bismuth (Bi) has two large principle peaks that are spin-orbit coupled:   Bi (4f7/2) and Bi (4f5/2)
  • Only the Bi (4f7/2) is used to check for the presence or absence of difference chemical states of Bismuth
  • The data-collector needed to analyze the chemical states of Bismuth for a sample, so he/she programmed the XPS instrument to collect data from 140 eV to 260 eV.
  • To resolve different chemical states that have a small chemical shift difference (~0.5 eV) the data-collector used a large X-ray spot size, a pass energy = 25 eV, with a step size of 0.1 eV, a 100 eV spectral window, and a dwell time of 50 msec.
  • These principle peaks are analyzed when the scientist wants to know what chemical states of bismuth exist on/in the surface of a sample. 
  • The two large peaks are due to photoelectrons coming from the Bi (4f7/2) and Bi (4f5/2) orbitals of pure Bismuth.
  • The small broad peaks are due to plasmons from pure Bismuth metal
  • At the base of the two strong peaks, we see sloping asymmetric lines attributed to valence-core electron interactions

Bi normal size



 

Topic #3:

Raw Chemical State Spectrum of Ionic Chlorine, “KCl”
that has Spin-Orbit Coupling

 

Features

  • Routine BE range (spectral window) is often 20-30 eV wide
  • Advanced spectrum analysis often requires a BE range between 50-150 eV to be able to analyze the satellites that exist for complex chemical state materials
  • Spin-orbit 2p pair with overlapping peaks
  • Cl (2p3/2) and Cl (2p1/2) orbitals with BE difference = 1.6 eV
A “simple” Chemical State Spectrum that involves spin-orbit coupled peaks – Cl (2p3/2) and Cl (2p1/2)

  • The high energy resolution, chemical state spectrum shown here is from a Chlorine (Cl) 2p signal due to Cl in a KCl crystal
  • Chlorine (Cl) has two overlapping principle signals that are spin-orbit coupled:  Cl (2p3/2) and Cl (2p1/2), BE difference = 1.6 eV
  • The data-collector needed to analyze the chemical states of Chlorine for a sample, so he/she programmed the XPS instrument to collect data from 185 eV to 270 eV.
  • To resolve different chemical states that have a small chemical shift difference (~0.3 eV) the data-collector used a large X-ray spot size, a pass energy = 25 eV, with a step size of 0.1 eV, a 100 eV spectral window, and a dwell time of 50 msec.
  • These principle peaks are analyzed when the scientist wants to know what chemical states of Chlorine exist on/in the surface of a sample. 
  • The two large peaks are due to photoelectrons coming from the Cl (2p3/2) and Cl (2p1/2) types of electrons in Chlorine.
  • The many small peaks are due to various “intrinsic states” due to special excitations in the Chlorine atom
  • A few elements have spin-orbit coupled signals that are difficult to resolve (e.g. Cl, Si, Al, S, P, Br)
  • In practice, we can find 2 types of Cl chemical states:  Ionic (bound to a metal) and Organic (bound to a Carbon). Ionic type Cl appears near 198 eV.  Organic type Cl appears near 200 eV.

Cl normal size



 

Topic #3:

Raw Chemical State Spectrum of Copper, Cu, metal
that has Spin-Orbit Coupling

Features

  • Two (2) large peaks
  • Cu (2p3/2) peak appears at 932 eV
  • Cu (2p1/2) peak appears at 952 eV
  • The energy difference between these two peaks is 20 eV
  • Four (4) very small peaks
  • These small peaks are called satellites or plasmons
A simple Chemical State Spectrum that has spin-orbit coupled peaks. Most XPS signals are spin-orbit coupled.

  • The high energy resolution, chemical state spectrum shown here is from pure Copper (Cu) metal.  
  • Copper (Cu) has two large principle peaks due to spin-orbit coupling:   Cu (2p3/2) and Cu (2p1/2)
  • Only the Cu (2p3/2) signal is used to check for the presence or absence of difference chemical states of Copper
  • The data-collector needed to analyze the chemical states of Copper for a sample, so he/she programmed the XPS instrument to collect data from 920 eV to 1050 eV.
  • To resolve different chemical states that have a small chemical shift difference (~0.5 eV) the data-collector used a large X-ray spot size, a pass energy = 25 eV, with a step size of 0.1 eV, a 130 eV spectral window, and a dwell time of 50 msec.
  • The principle signal Cu (2p3/2) is analyzed when the scientist wants to know what chemical states of copper exist on/in the surface of a sample.  It is possible for the spectrum of Copper to have from 1 to >20 peaks (due to multiplet splitting effects)
  • The two large peaks are due to photoelectrons coming from the Cu (2p3/2) and Cu (2p1/2) orbitals of pure copper.
  • The BE of Cu (2p3/2) photo-electrons appear at 932.67 eV and the BE of Cu (2p1/2) photo-electrons appear at 952.47 eV
  • The various small peaks are due to plasmons from pure Copper metal

Cu normal size



Copper (Cu) Continued 

 

Features

  • Because CuO is conductive, there is no need to use the electron flood gun to charge neutralize the sample.  The BEs obtained are peak-fitting this sample are true BEs and do not need correction because the material sis conductive.

A Very Complex chemical state spectrum

from the Cu (2p) Signal of Copper (II) Oxide, CuO
that shows Spin-Orbit Coupling

  • This raw chemical state spectrum was obtained from a literature journal (Surface Science Spectra).
  • This is a Cu (2p) spectrum from Cupric Oxide (CuO) that shows peaks from both the Cu (2p3/2) and Cu (2p1/2) signals
  • The Cu (2p3/2) peak at ~933.6 eV is due to the CuO chemical state. Note:  Pure copper metal appears at ~932.7 eV.
  • Only the Cu (2p3/2) is used to check for the presence or absence of difference chemical states of Copper
  • The BE chemical shift for CuO relative to pure Copper metal is ~1 eV
  • The noisy wide peak between ~940-944 eV is often called a “shake-up” peak.  It’s shape is used as a characteristic indicator.
  • Due to a “final state” effect, all “4” of the peaks are affected by “multiplet splitting” which means that each peak actually has a series of peaks that are due to interactions between an unpaired valence electron and other electrons deeper inside the Copper atom.  This spectrum looks easy to peak-fit but actually is difficult and requires many constraints.
  • To peak-fit this spectrum properly, the data-analyst would have to use various advanced level peak-fitting constraints including:  FWHM constraints, peak area ratio constraints, BE position constraints.

 



 

Topic #4 – Which XPS Signals are used to measure Chemical State Spectra?

and Why?

 



 

Essential BASIC Information about Chemical State Spectra
Before looking at any new type of spectral data, scientists need to ask a few basic questions and to visualize various key terms / phrases.

 

Question:  Are the following “features” identical ?
Does  Signal” = “Peak” = “Spectrum?

Answer:  No

 

Science Terminology

  • Signal:  an impulse, or an action that conveys data or information.
  • Peak:  the pointed top (of a mountain)
  • Spectrum:  a collection of colors, as seen in a rainbow, or a range of energies
  • Principle:  the term “principle” has the same meaning as “main”, i.e. Principle Signal = Main Signal
  • Chemical State:  the term “chemical state” has the same meaning as “chemical species”. Go to “Chemical State Definition” for explanation.

XPS Terminology

  • Signal:  the O (1s) type of photo-electrons is a characteristic type of Principal XPS Signal. The O (1s) signal appears at 532 eV.  Each Principle XPS Signal has a single FWHM that can range from 0.3 to 3.0 eV in width.  Other examples of Principle XPS Signals are:   C (1s), Si (2p), Fe (2p3), Au (4f7), U (3d5).  A single XPS Signal can produce multiple XPS Peaks within a single XPS Spectrum. Those multiple component peaks can be due to the presence of different chemical states / chemical species. This is the major reason why many people use XPS.  They use XPS to find different Chemical States on a surface.
  • Peak:  an XPS Peak is due to just one particular type (or kind) of a chemical material, a chemical species. An XPS Spectrum often has 2 or more XPS peaks.  XPS Spectra can have 2 XPS Peaks that are separated by 0.5 eV or > 20 eV.
  • Spectrum:  a range of binding energies (20-100 eV for chemical state spectra) plotted against the count-rate (or total counts) of photo-electrons emitted is an XPS Spectrum. An XPS Spectrum is a range of BEs within which a single XPS Signal can produce one or more component XPS Peaks that represent one or more different Chemical States / Chemical Species.  In special cases, there are overlaps of different XPS Signals which complicates interpretation.
  • “s”, “p”, “d”, and “f”:  are the different types of electron orbitals that are measured by XPS.  The “shell” number of an atom and the “orbital” type of an atom form part of the abbreviation (designation) that is used to describe Principal XPS Signals.
  • Shell Numbers: range from 1-6 for peaks observed when using Aluminum X-rays (E=1486.7 eV)
  • Spin-Orbit Splitting (Coupling) Terms can be:  1/2, 3/2, 5/2, 7/2.  These terms are shown as sub-scripts  (1/2, 3/2, 5/2, 7/2) just after the electron orbital type (p3/2 or d5/2 or f5/2)

 

Examples of XPS Terminology

Signal Peak Spectrum
 

 



 

Topic #4

Which XPS Signals are used to measure Chemical State Spectra? – Continued

Question:  Why are Principle XPS Signals used to collect Chemical State Spectra?

  • The number of XPS Signals produced by an element varies from 2 to 15 when the X-ray source is Al K-alpha which has an Energy = 1486.7 eV. Light elements (low Z) produce 2-5 obvious XPS signals.  Heavy elements (Z >55) produce 8-15 XPS signals.  Which XPS Signal for an element is the best to use to measure Chemical States that element?
  • Principle (Main) XPS Signals have the smallest (narrowest) FWHM (peak-width) so they are the best to use to resolve the presence or absence of different chemical states in a Chemical State Spectrum.  All other XPS signals for that element have larger FWHM.
  • Principle (Main) XPS Signals are usually the most intense XPS signal(s) for an element. This signal usually has the largest SF (RSF or ASF) value.
  • Because the Principle (Main) Signal has the most narrow FWHM, the Principle XPS Signal can provide more accurate and useful chemical state information.
  • Because the Principle XPS Signal has the most narrow FWHM, the component-peaks have less peak overlap, and allow us to better resolve the presence or absence of more chemical states.
  • Principle (Main) Signals are used to identify the presence or absence of different chemical state spectra because many other scientists over the past 60 years have used the same principle signals to identify and assign chemical states to the characteristic BEs that are resolved from peak-fitting the chemical state spectrum of interest.  These Reference BEs are useful guides.  The NIST XPS Database has a collection of BEs, no spectra.  The PHI handbook and the Crist Handbook are useful reference sources of BEs and actual spectra. The XPS Library has an extensive list of Reference BEs useful for Chemical State Assignments.
  • Other examples of Principle XPS Signals are:   C (1s), Si (2p), Fe (2p3), Au (4f7), U (3d5)…..
  • A Periodic Table of Principle XPS Signals (shown below) lists the BE of the pure element and the type of Principle XPS Signal that is normally used when we want to measure chemical state spectra.  The BE that you see, should be used to help select the range of BEs to be analyzed.  The range of BEs is typically 10-15 eV below the BE shown and also 10-15 eV above the BE shown.  This makes a spectrum that has a 20-30 eV range of BEs.
  • Because nearly all chemical states appear at higher BE than the BE of the pure element, the BE range of the spectrum is adjusted slightly so that the pure element peak BE appears at 2-3 eV to the right at lower BE,  That way the raw data appears almost uniformly on the spectrum.

 

Details about Principle Signals, BEs of Chemicals States, Electronegativity

  • A Chemical State Spectrum is also known as a High (Energy) Resolution Spectrum, or a Narrow Scan. A chemical State Spectrum is usually 20-100 eV wide.
  • The range of Chemical State BEs produced by a single element, bonded to 1-2 other elements, can range from ~1 eV to 12 eV due to differences in electronegativity of the elements in the group and the type of chemical bonds (single, double, triple),
  • As an example:  Carbon bound to Oxygen, Nitrogen, Sulfur and other elements with different bonds produce chemical state peaks that appear between 282 eV and 294 eV.
  • Chemical State Spectra can have multiple XPS Peaks that are due to two different elements bonded together and having electronegativity differences.
  • Differences in Electronegativity between two elements have a direct effect on the chemical state BE and the chemical shifts of both elements.

 

Rules of Thumb – Basic Guidelines to help with peak-fitting and identifying different Chemical States

  • Chemical State Shifts usually ~1 eV
  • Differences in Chemical States is usually ~ 1 eV
  • FWHM for the Principle peak of a pure Elements is usually ~1 eV
  • FWHM for the Principle peak of a Chemical Compounds is usually ~1.5- 1.8 eV

 



 

Topic #4

Which XPS Signals are used to measure Chemical State Spectra? – Continued

 

Table of Principal XPS Signals:  useful to define Binding Energy Ranges

Use the BE of a signal as the center of your spectrum.  Make your spectrum 20-30 eV wide.  To study the loss and satellite features expand BE to 100 eV.
Keep in mind that most oxidation state BEs are 2-3 higher than the pure element BE.

 

 

 

 



 

Topic #5  –  Features of Peak-fitted Chemical State Spectra

 



 

 

Features of a Peak-fitted Chemical State Spectrum 

Features of a Peak-fit

  • If sample is non-conductive, then BEs are charge referenced to hydrocarbon C (1s) BE or Au (4f7) due to a gold dot on the sample
  • If the hydrocarbon C (1s) peak is used for charge referencing all other peak BEs, then the hydrocarbon C (1s) peak is usually between 284.6 and 285.0 eV. There is no standard BE for this peak BE.
  • Each peak (signal) has a BE (eV) measured from the peak maximum BE.
  • Each peak has a FWHM.
  • Each peak has a Relative Area
  • Each peak has a chemical state peak assignment made by the XPS data-scientist
  • This peak-fit uses 4 synthetic peaks to fit the raw peak-envelop
  • Each peak has a chemical shift with respect to the “Principal” peak
  • A background was added, usually an iterated Shirley background
  • Each peak has a peak-shape that is composed of Gaussian and Lorentzian peak-shapes.  The % of Gaussian is often 70-90%, while the Lorentzian % is often 10-30%.
  • In advanced software, the peak-shapes are Voigt shaped that report a Gaussian FWHM and a Lorentzian FWHM for each peak.
  • A peak-fit normally reports a (reduced) Chi-Square value which indicates the goodness of the synthetic peaks to the peak envelop produced by the raw data

 



 

Topic #6:  Useful Reference BE Tables, Chemical Shift Chart
to assist Peak-fitting of Chemical Compounds

 



 

 

Reference Table of BEs and FWHMs to Assist Peak-fitting of Chemical Compounds

 

Alt_text

 

 



 

Topic #6:  Useful Reference BE Tables, Chemical Shift Chart
to assist Peak-fitting of Chemical Compounds

 

Reference Table to Assist Chemical State Assignments of Component Peaks
due to different types of Carbon or Carbon Compounds

 

 



 

Electronegativity Table for Reference Purposes

 

 

 



 

Topic #6:  Useful Reference BE Tables, Chemical Shift Chart
to assist Peak-fitting of Chemical Compounds

 



 

Summaries of NIST BEs from Chemical Counpounds
used to Assign Chemical States
(assembled by Mark Beisinger)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



 

How do we use Chemical State Spectra?

 

Common Questions

  • What can Chemical State Spectra tell us?
  • How can we use Chemical State Spectra?
  • What information can we derive from Chemical State Spectra?
  • Why do we collect Chemical State Spectra?
  • What is the purpose or goal of identifying chemical state spectra?
  • Are High Res Spectra the same as Chemical State Spectra?