1. Infrared Spectra and Calculated Binding Energies of γ-butyrolactone Dimers and Trimers
69th annual international symposium on molecular spectroscopy
Eric Willis, Chris Baumann
June 19, 2014
RI07

2. Optimized Structure of γ-butyrolactone UM06/6-311++(2d,p)
Bond lengths (Å)
R12 = 1.189, R62 = 1.353, R56 = 1.426
Angles (°)
∠123 = 128.6, ∠126 = 122.6, ∠623 = 108.8, ∠562 = 110.7
Dihedral Angles (°)
∠1234 = 162.8, ∠1265 = 177.2

3. αβ Dimer

4. αγ Dimer

5. βγ Dimer

6. γγ Dimer

7. Dimer Structural Changes
Elongation of C=O bond observed in all species
Cγ – O bond elongated in all species
Carbonyl C-O bond shortened in case of γγ and βγ dimers
Several bond angle alterations observed in dimers
Centered around carbonyl group and ring oxygen
Dihedral angle changes indicating changes in ring puckering
Increased puckering on one side, decreased on the other

8. αγγ Ring Trimer

9. αβαγ Stacked Trimer Changes magnified in middle unit
Dihedral angles almost unchanged throughout the molecule.

10. The Covalent Trimer

11. Binding Energy (kJ/mol) Counterpoise Correction (kJ/mol)
Energy Information
Species
Energy (kJ/mol)
Binding Energy (kJ/mol)
Counterpoise Correction (kJ/mol)
Monomer --
αβ Dimer
58.85
3.60
αγ Dimer
57.60
3.50
βγ Dimer
57.74
3.03
γγ Dimer
55.25
3.29
αγγ Ring Trimer
68.81
6.46
αβαγ Stacked Trimer
74.08
7.36
Covalent Trimer
228.85

12. Matrix Isolation Process
GBL deposited on nitrogen at 20 K
Cooled down to 12 K
Photolysis
Annealing

13. Monomer Spectrum

14. Dimer Spectra

15. αγγ Spectrum

16. αβαγ Stacked Trimer

17. Comparison with Experimental Spectrum (13 K)

18. Carbonyl Region Close-up

19. Pre-Annealing

20. Post-Annealing

21. Results of Experimental Spectral Analysis
Dimer and trimer peaks can be differentiated, however individual dimer and trimer structures can’t be resolved
Relative amount of dimer and trimer increases with annealing
Photolysis affects ratio as well

22. Deuterated Difficulties

23. Anharmonic Corrections
Type of Transition
Frequency (cm-1)
Intensity (km mol-1)
Overtone (v17)
1847.5
60.0
Combination Band (v20 + v12)
1869.8
63.5
Combination Band (v20 + v13)
1866.3
18.3
Combination Band (v21 + v11)
1851.8
13.8
Combination Band (v23 + v10)
1868.1
14.6
Combination Band (v25 + v8)
1856.6
70.5
Several combinations and overtones in this region can contribute to the messiness in the carbonyl region for the deuterated spectrum

24. Electronic Spectroscopy
Monomer
Excited State
State
Energy (eV)
Wavelength (nm)
Oscillator Strength S2 1
3.000-A
5.4293
228.36 2
1.000-A
5.7507
215.6
0.0008 3
5.8472
212.04 4
5.898
210.22
0.0023 5
6.0806
203.9 6
6.3386
195.6
αβ Dimer
αγ Dimer
Excited State
State
Energy (ev)
Wavelength (nm)
Oscillator Strength S2 1
3.000-A
5.4822
226.16 2
5.5095
225.04 3
1.000-A
5.8072
213.5
0.0004 4
5.8294
212.69
0.0007 5
6.0303
205.6 6
6.0476
205.01 7
6.0691
204.29
0.0028 8
6.0924
203.51
0.0022 9
6.0983
203.31 10
6.1157
202.73 11
6.267
197.84 12
6.2915
197.07
Excited State
State
Energy (ev)
Wavelength (nm)
Oscillator Strength S2 1
3.000-A
5.5058
225.19 2
5.5268
224.33 3
1.000-A
5.8378
212.38
0.0002 4
5.8604
211.56
0.0004 5
6.0253
205.77 6
6.0566
204.71 7
6.0573
204.68
0.0024 8
6.0905
203.57
0.0017 9
6.1194
202.61 10
6.1556
201.42 11
6.2555
198.2 12
6.2705
197.73
0.0018

25. βγ Dimer αγγ Trimer γγ Dimer Excited State State Energy (ev)
Wavelength (nm)
Oscillator Strength S2 1
3.000-A
5.4865
225.98 2
5.4911
225.79 3
1.000-A
5.8171
213.14
0.0004 4
5.8251
212.84
0.0005 5
6.0585
204.65 6
6.0623
204.52 7
6.0807
203.9 8
6.09
203.59 9
6.0985
203.3
0.0007 10
6.1254
202.41
0.0042 11
6.2771
197.52 12
6.2893
197.13
0.0014
αγγ Trimer
Excited State
State
Energy (ev)
Wavelength (nm)
Oscillator Strength S2 1
3.000-A
5.5602
222.99 2
5.5687
222.65 3
5.5771
222.31 4
1.000-A
5.8732
211.1
0.0009 5
5.8761
211
0.0017 6
5.8883
210.56
0.0012 7
5.9723
207.6 8
5.9775
207.42 9
6.0071
206.4 10
6.0122
206.22
0.0015 11
6.0239
205.82
0.0025 12
6.0529
204.84
0.0048 13
6.1121
202.85 14
6.1197
202.6 15
6.1422
201.86 16
6.2356
198.83 17
6.2446
198.55 18
6.2504
198.36
γγ Dimer
Excited State
State
Energy (ev)
Wavelength (nm)
Oscillator Strength S2 1
3.000-A
5.4809
226.21 2
5.4838
226.09 3
1.000-A
5.8117
213.33 4
5.8218
212.97
0.0008 5
6.0329
205.51 6
6.056
204.73 7
6.0871
203.68 8
6.1076
203 9
6.1182
202.65
0.0003 10
6.145
201.77
0.0045 11
6.322
196.12 12
6.3361
195.68
0.0027

26. αβαγ Trimer Covalent Trimer Excited State State Energy (ev)
Wavelength (nm)
Oscillator Strength S2 1
3.000-A
5.4822
226.16 2
5.4857
226.02 3
5.5916
221.73 4
1.000-A
5.804
213.62
0.0005 5
5.8105
213.38
0.0003 6
5.9208
209.4 7
5.9597
208.04 8
5.9775
207.42 9
5.9918
206.92
0.0023 10
6.0047
206.48 11
6.0179
206.03
0.0018 12
6.0309
205.58
0.0024 13
6.09
203.59 14
6.1112
202.88 15
6.175
200.79 16
6.2673
197.83 17
6.2782
197.48
0.0007 18
6.2895
197.13
Excited State
State
Energy (ev)
Wavelength (nm)
Oscillator Strength S2 1
3.000-A
5.6354
220.01 2
5.6367
219.96 3
1.000-A
5.663
218.94
0.0006 4
5.6642
218.89 5
5.8073
213.5 6
5.8387
212.35
0.0036 7
5.8994
210.17 8
5.9248
209.26
0.0011 9
5.9379
208.8 10
5.9387
208.77 11
5.955
208.2
0.0008 12
5.9558
208.17 13
6.0737
204.13 14
6.0742
204.11 15
6.1008
203.22
0.0026 16
6.1016
203.2 17
6.2411
198.66 18
6.2415
198.65

27. Summary/Conclusions
Structural changes observed in monomer units when dimer and trimer species are formed
Dimers and trimers can be detected experimentally using vibrational spectroscopy
However, individual dimer and trimer species cannot be resolved
Complicated nature of carbonyl region may be due to combination bands and overtones

28. What’s Next? GBL + H2O complexes
Selective photodissociation of trimers and dimers as a possibility
More accurate calculations
Creating more trimer structures and higher multimers