![FTIR Spectroscopy
University of California at Davis Chemistry Department. FTIR Block Diagram [Image]
Retrieved April 14, 2015.
• Time domain data to
frequency domain data
• Need fast time scales
• Light is split and reflected
off a motorized mirror
• Fourier transforms
interferogram into a
spectrum](https://image.slidesharecdn.com/a7823741-af04-4e23-87ed-c781b6f7f720-150829044954-lva1-app6891/85/Compiled-presentations-MOS-3-320.jpg)
![Emission
Microscopy Resource Center. Jablonski Energy Diagram; Excitation and Emission
Spectrum [Image] Retrieved April 14, 2015.
• ΔE = hν
• Use single wavelength
to excite to a particular
excited state
• Electrons relax back to
various vibrational
levels in the ground
state
• Provides information
concerning the ground
state](https://image.slidesharecdn.com/a7823741-af04-4e23-87ed-c781b6f7f720-150829044954-lva1-app6891/85/Compiled-presentations-MOS-9-320.jpg)
Compiled presentations MOS
- 1. Molecular Spectroscopy B Y: L E L A N D B R E E D L O V E , A N D R E W H A R T F O R D , R O M A N H O D S O N , A N D K A N D Y S S N A J J A R
- 2. R O M A N H O D S O N Theory and Introduction
- 3. FTIR Spectroscopy University of California at Davis Chemistry Department. FTIR Block Diagram [Image] Retrieved April 14, 2015. • Time domain data to frequency domain data • Need fast time scales • Light is split and reflected off a motorized mirror • Fourier transforms interferogram into a spectrum
- 4. Rotational/Vibrational Energy Levels Vibrational Energy: Rotational Energy: G(v) = (v + ½)νe F(J) = BJ(J+1) MIT. (n.d.). Principles of Molecular Spectroscopy. Retrieved March 23, 2015, from http://web.mit.edu/ 5.33/www/lec/spec4.pdf. • Rotational levels nested between vibrational levels • J is rotational quantum number, v is vibrational quantum number • Total energy is the sum of the two • Selection rules
- 5. P and R Branches UC Davis. (n.d.). Rovibrational Spectroscopy. Retrieved April 14, 2015, from http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Rotational_Spectroscopy/ Rovibrational_Spectroscopy • Higher rotational levels can be populated at room temperature • ΔJ = +1, rotational transition added to vibrational energy (R) • ΔJ = -1, low wavenumber side of branch (P)
- 6. Harmonic Oscillator University of Liverpool. (n.d.). Vibrational Spectroscopy. Retrieved March 13, 2015, from http://osxs.ch.liv.ac.uk/java/spectrovibcd1-CE-final.html. • All energy level spacing is equal (hν) • Equilibrium bond length is the same at all energy levels • Forbids vibrational transitions of Δv ≠ ± 1 • Does not account for bond dissociation/repulsion
- 7. Anharmonic Oscillator University of Liverpool. (n.d.). Vibrational Spectroscopy. Retrieved March 13, 2015, from http://osxs.ch.liv.ac.uk/java/spectrovibcd1-CE-final.html. • Shows equilibrium bond length changes • The spacing between energy levels decreases at higher quantum numbers • Models bond dissociation/repulsion • Allows for overtone transitions: Δv > ±1
- 8. Absorption • ΔE = hν • A = εlc • A = -log(I/Io) • Use range of wavelengths • Provides information about the excited state energy levels UC Davis. (n.d.). Infrared: Theory. Retrieved April 14, 2015, from http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Vibrational_Spectroscopy/Infrared_Sp ectroscopy/Infrared%3A_Theory
- 9. Emission Microscopy Resource Center. Jablonski Energy Diagram; Excitation and Emission Spectrum [Image] Retrieved April 14, 2015. • ΔE = hν • Use single wavelength to excite to a particular excited state • Electrons relax back to various vibrational levels in the ground state • Provides information concerning the ground state
- 10. Franck-Condon Principle UC Davis. (n.d.). Selection Rules and Transition Moment Integral. Retrieved April 14, 2015, from http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Fundamentals/ Selection_rules_and_transition_moment_integral • Born-Oppenheimer approximation • Demonstrates vibronic transitions • The wavefunctions in ground and excited state must overlap • Peak intensity is proportional to amount of overlap
- 11. Analysis of carbon monoxide through its rovibrational spectrum A N D R E W H A R T F O R D
- 12. Experimental method Evacuated and collected background spectrum of gas sample cell using FTIR spectrophotometer Filled sample cell with 100 mmHg CO, collected spectra at resolutions of 4, 2, 1, 0.5, 0.25 cm-1 Stored gas sample in desiccator when not in use
- 13. Results 2728 -28 26 -27 25 -26 24 23 -25 -24 22 21 -23 20 -22 19 18 -21 -20 17 16 -19 15 -18 1113 -17 14 12 -16 -15 -14 -13 8 -12 10 -11 9 -10 7 -9 -8 6 -7 5 -6 -5 4 3 -4 -3 2 1 -2 -1 1 0 2 1 3 4 2 5 43 6 5 7 6 8 7 9 8 10 9 11 10 12 11 13 12 14 13 15 14 16 17 1516 18 19 17 20 18 21 19 22 22 23 20 24 21 25 23 26 27 25 24 26 28 27 29 28 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 2000 2050 2100 2150 2200 2250 Absorbance(AU) Wavelength (cm-1) P-Branch R-BranchP-Branch R-Branch J values Fundamental Absorbance Spectrum (CO) between 1950-2275 cm-1
- 14. First overtone (CO) between 4100-4400 cm-1 24 -24 23 -23 22 -22 21 20 -21 -20 19 -19 18 -18 17 16 -17 15 14 -16 12 -15 13 -14 -13 -12 11 -11 10 -10 9 8 -9 -8 7 -7 6 4 -6 5 -5 3 -4 2 -3 1 -2 -1 0 1 2 1 3 2 4 3 5 6 4 5 7 6 8 9 7 10 9 11 8 10 12 13 14 12 11 15 13 16 14 15 17 18 19 20 16 18 21 17 19 22 23 20 22 21 24 25 23 24 0.08 0.1 0.12 0.14 0.16 0.18 0.2 4125 4175 4225 4275 4325 Absorbance(AU) Wavelength (cm-1) P-Branch R-Branch J-values
- 15. Wavelength vs. m values (Fundamental spectrum) y = -6E-05m3 - 0.0143m2 + 3.7663m + 2142.8 R² = 0.9997 y = -0.0143m2 + 3.7376m + 2142.8 R² = 0.9997 y = 3.7234m + 2138.7 R² = 0.9964 2000 2050 2100 2150 2200 2250 -30 -20 -10 0 10 20 30 Wavelength(cm-1) m values Cubic Quadratic Linear
- 16. Wavelength vs. m values (First overtone spectrum) y = 3.7673m + 4252.2 R² = 0.9862 y = -0.0349m2 + 3.8018m + 4259.6 R² = 1 y = -1E-05m3 - 0.0349m2 + 3.8058m + 4259.6 R² = 1 4100 4150 4200 4250 4300 4350 -30 -20 -10 0 10 20 30 Wavelength(cm-1) m values Linear Quadratic Cubic
- 17. Constatnts Fundamental (cm-1) First Overtone (cm-1) 2142.9 4259.6 Equilibrium Frequency (cm-1) αe (cm-1) Be (cm- 1) De (cm-1) χe (cm- 1) Experimental Value 2168.8 0.0143 1.90 1.5 x 10- 5 0.00599 Literature Value19 2169.8 0.0175 1.9313 6.2 x 10-6 0.00612 Percent error 0.0461% 18.3% 1.62% 142% 2.12%
- 18. Molecular constants Moment of Inertia (kg m2) Equilibrium bond (Å) Force Constant (N/m) Experimenta l Value 1.47 x 10-46 1.14 1903 Literature Value19 1.4490 x 10-46 1.1281 1902 Percent error 1.45% 1.05% 0.0526%
- 19. Global Warming Potentials of Greenhouse Gases Kandyss Najjar http://commons.wikimedia.org/wiki/File:Earth's_greenhouse_effect_(US_EPA,_2012).png
- 20. Brief Theory GWP - heat trapped by greenhouse gases when exposed to IR radiation emitted from the Earth quantity, strength, and location of IR absorption bands Researchers and political activists – effects on climate change Radiation forcing capacity – sum of IR spectrum and emission of Earth blackbody radiation Equivalent to the GWP relative to gas atmospheric lifetime RFC can be determined relative to a reference gas Normally CO2 **Elrod, M. J. J. Chem. Ed. 1999, 76, 1702-05.
- 21. Brief Theory (Cont.) The radiation forcing capacity is given by Equation 1 RFA – radiation forcing capacity per 1 kg increase of sample A(t) – time decay of a pulse of sample RFR and R(t) – same, but for reference Equation 2 – determine GWP in terms of mass instead of molecule τ – atmospheric lifetime (years) MW – molecular mass (g/mol) Equation 1 Equation 2 **Elrod, M. J. J. Chem. Ed. 1999, 76, 1702-05.
- 22. Experimental NaCl cell evacuated as per Week 1’s procedure Using OMNIC – background spectrum Range: 495 – 1600 cm-1 Resolution: 1 cm-1 Filled gas cell with: CH4 – 60.0 Torr N2O – 60.1 Torr IR spectra taken for both gases Range: 495 – 1600 cm-1 Resolution: 1 cm-1 http://www.specac.com/assets/products/49903cada5f6c.jpg
- 23. Expected Results Nitrous Oxide Fundamental: ~600 cm-1 First Overtone: ~1300 cm-1 Methane First Overtone: ~ 1200 cm-1 to ~ 1400 cm-1 N2O CH4 Molecular Spectroscopy. University of Texas at Austin - Chemistry Department. Canvas.utexas.edu (accessed April 26, 2015).
- 24. Experimental Results IR spectra obtained were very similar to the expected spectra Nitrous Oxide Fundamental: ~600 cm-1 1st Overtone: ~1300 cm-1 Methane 1st Overtone: ~ 1200 cm-1 to ~ 1400 cm-1 -0.10 0.10 0.30 0.50 0.70 0.90 495.00 695.00 895.00 1095.00 1295.00 1495.00 Absorbance(AU) Wavenumber (cm-1) N2O -0.05 0.15 0.35 0.55 0.75 0.95 495.00 695.00 895.00 1095.00 1295.00 1495.00 Absorbance(AU) Wavenumber (cm-1) CH4
- 25. Calculating Global Warming Potential (GWP) Converted IR spectra to CSV files Using Excel, constructed table 505 – 1495 cm-1, in increments of 10 cm-1 =lookup function to add corresponding IR absorbance data Inserted table into provided “Global Warming Potential Model” spreadsheet Path length: 10 cm Lifetime, formula weight, and gas pressure in cell** N2O – 120 years, 44.01 g/mol, 60.1 Torr CH4 – 15 years, 16.04 g/mol, 60.0 Torr Time Horizons: 20, 100, and 500 years **Elrod, M. J. J. Chem. Ed. 1999, 76, 1702-05.
- 26. Results GHG Lifetime (Years)** Time Horizon (Years) Calculated GWP Literature GWP** Percent Difference (%) N2O 120 20 73.3 93 21.1 100 69.3 88 21.3 500 60.9 77 20.9 CH4 15 20 33.3 37 10.0 100 11.6 13 10.9 500 5.9 6 2.46 **Elrod, M. J. J. Chem. Ed. 1999, 76, 1702-05.
- 27. Short Summary IR spectra obtained match expected spectra Nitrous Oxide Fundamental: ~600 cm-1 1st Overtone: ~1300 cm-1 Methane 1st Overtone: ~ 1200 cm-1 to ~ 1400 cm-1 N2O is a more effective greenhouse gas Larger atmospheric lifetime Larger GWP more efficient at trapping heat within atmosphere
- 28. L E L A N D B R E E D L O V E Absorbance And Emission Of Iodine Gas
- 29. Experimental I2 absorption spectra Halogen lamp Detector inline with beam I2 emission spectra Argon LASER Detector arranged 90° to laser Filter used to maximize area of interest
- 30. Absorption
- 31. I2 Absorption Bandhead Energy versus v’ + ½ y = -0.0076x3 - 0.4381x2 + 119.23x + 15690 R² = 0.9999 16500 17000 17500 18000 18500 19000 19500 20000 0 10 20 30 40 50 60 70 80 90 Wavenumbers(cm-1) v' + 1/2
- 32. Emission 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 34 36 0 5000 10000 15000 20000 25000 500 550 600 650 700 750 800 Intensity Wavelength (nm)
- 33. I2 Emission Bandhead Energy vs v” + ½ y = -0.0012x4 + 0.0754x3 - 2.1404x2 + 224.93x - 138.15 R² = 1 0 1000 2000 3000 4000 5000 6000 7000 8000 0 10 20 30 40 50 60 70 80 Wavenumber(cm-1) v" + 1/2
- 34. B-State and X-State Constants Spectroscopic constants Experimental values (cm-1) Literature Values12 (cm- 1) Percent Error (%) G”(0) 138.15 107.11 29.0 v”e 224.93 214.53 4.85 vex”e 2.14 0.6130 249 vey”e -0.5177 0.0754 73303.88 D”o 11731.229 12440.2 5.70 E(I*) 7927.4 7602.98 4.27 Spectroscopic constants Experimental values (cm-1) Literature Values12 (cm-1) Percent Error (%) G”(0) 138.15 107.11 29.0 v”e 224.93 214.53 4.85 vex”e 2.14 0.6130 249 vey”e -0.5177 0.0754 73303.88 D”o 11731.229 12440.2 5.70 E(I*) 7927.4 7602.98 4.27
- 35. B-State Morse Potentials Spectroscopic constants Experimental Values Literature Values12 Percent Error (%) D’ e 3968.578 cm-1 4381.2 cm-1 9.42 R’e Used Lit. Value 3.0267 Å n/a Te 15828.15 cm-1 15769.1 cm-1 0.374 v’e 84.603 cm-1 125.67 cm-1 32.7
- 36. Morse Potential plots FCintensity
- 37. Discussion Morse potentials show longer eq. bond length for X- state than B-state ----Not good Data shows less transitions than literature predicts largest Franck-Condon factor from the emission spectrum at v” = 5, at 544 nm The results from our calculations are more reliable than FCIntensity values equilibrium bond length of the X-State is less than that of the B-State
- 38. Questions?
Editor's Notes
- #2: Studies the response of molecular structure to electromagnetic radiation
- #4: Timescales are too short, so need to use an interferometer. Difference of the intensity of these two beams are measured as a function of the difference of the paths
- #5: Takes more energy to excite from one vibrational energy level to another. B is rotational constant in wavenumbers.
- #6: +1, rotational quant number in excited state is 1 more than quant number in ground state -1, rotational quant number in ground state is 1 more than quant number in excited state Q branch, both rotational quant numbers are equal
- #7: Parabolic symmetry
- #8: Average bond length increases during vibrational state transition n > 1 Overtone is ground vibrational state to second vibrational state
- #9: Populations based on Boltzmann distribution
- #11: Mass of nuclei large compared to electrons, so used as a fixed point. Vibronic modes excited
- #30: Dark and light backgrounds taken detector placed perpendicular to beam to prevent saturation filter in front of the path of the laser to maximize the region of interest as well as to minimize the laser signal adjusting the signal to noise ratio by increasing the number of scans.
- #31: The bandheads show the vibronic transitions from the ground state to varying excited states. These bandheads are where the unresolved vibrational-electronic lines are the strongest. We then plotted the bandhead energy versus v’ + ½ (Figure 21) which provided us with a cubic fit, which we then used to calculate the spectroscopic constants for the B-State anharmonicity constants, vex’e and vey’e. The error in this part of the data analysis is due to the extrapolation of the cubic fit in order to find the maximum of the function, which corresponds to De. In addition, even though the R2 is practically equal to 1, there is always estimation error associated with extrapolation, which can lead to erroneous results, particularly in the case of the anharmonicity constants.12
- #33: Emission where larger values of v” correspond to higher energy vibronic levels plotted the bandhead energies versus v” + ½ to find the spectroscopic constants of the X-State Again anharmonicity and Extrapolation of the fourth order fit is the cause of this error
- #35: anharmonicity constants, vex’e and vey’e. The error in this part of the data analysis is due to the extrapolation of the cubic fit in order to find the maximum of the function, which corresponds to De. In addition, even though the R2 is practically equal to 1, there is always estimation error associated with extrapolation, which can lead to erroneous results, particularly in the case of the anharmonicity constants.12 Extrapolation of the fourth order fit is the cause of this error
- #36: E= Te+ De(1-e(β(R-Re))^2 β= νeπ(2μc/hDe)^1/2 R is bond length (Å), Re is equilibrium bond length (Å), μ is the reduced mass of molecular iodine (g), νe is the equilibrium frequency (cm-1), h is Planck’s constant (J s), and c is the speed of light (m/s)