1. A PROTOCOL FOR HIGH-ACCURACY THEORETICAL THERMOCHEMISTRY
Bradley Welch and Richard Dawes

2. Introduction What is the Active Thermochemical Tables (ATcT)
Branko Ruscic,Argonne National Laboratory
Methyl Peroxides and Methyl Hydroperoxide
High Accuracy Composite Approach
Vibrational Perturbation Theory 2 Results
Level Derived Quantities
Conclusions

3. What are the Active Thermochemical Tables (ATcT)D0 C EA F2 IE F Eq CO cC
C (grph)
H2O2 (l)
DvH
CH3+
Hyd H2 O2
H2O (l)
CO2
CH3OH (l)
rGPA HF F–
H2O
OH–
CH3OH
CH3 O
CH2O H
CH3O
CH3O–
DsH
CH2O (s) AE
CH4 OH
OH+
TAE0
H2O2
IPF H+

4. What are the Active Thermochemical Tables (ATcT)
CH3O2H (+/ kcal/mol)
B. Ruscic and D. H. Bross, Active Thermochemical Tables (ATcT) values based on ver of the Thermochemical Network (2016); available at ATcT.anl.gov

5. Methyl Peroxide and Hydroperoxide
Relevant to atmospheric and combustion chemistry
Smallest members of alkyl peroxide and hydroxide families
Not well represented in the ATcT. Larger alkyl’s are not present

6. Methyl Peroxides cont.
Methyl Peroxides have an anion, radical, and cationic species
Methyl Peroxide anion (1A´) and Methyl Hydroperoxide (A) are singlet species
Methyl Peroxide radical is a doublet (2A´´) while the cation is a triplet species (3A´´)

7. High Accuracy Composite Approach1,2,3
Make use of explicitly correlated CCSD(T) for rapid CBS convergence
𝐸 𝐶𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 = 𝐸 𝐻𝐹−𝐶𝐴𝐵𝑆 𝑐𝑞𝑧−𝑓12 + 𝐸 𝐶𝐶𝑆𝐷 𝑇 −𝑓12𝑏 𝑐𝑡𝑧−𝑓12→𝑐𝑞𝑧−𝑓12 + 𝐸 𝑟𝑒𝑙 + 𝐸 𝑍𝑃𝑉𝐸 + 𝐸 𝐷𝐵𝑂𝐶
CCSD and (T) terms were extrapolated to CBS
ZPVE was computed with Vibrational Perturbation Theory 2(VPT2) to obtain an anharmonic ZPVE. Different methods for the VPT2 portion were considered due to expensive computational costs with CCSD(T)-F12b4
1.A.Tajti,  P.G. Szalay, A.G.  Csaszar,  M.   Kallay, J.  Gauss,  E.F.  Valeev,  B.A.  Flowers, J.  Vazquez J.F. Stanton J. Chem.  Phys.  121, (2004)
2. M. S. Schuurman, S. R. Muir, W. D. Allen, and H. F. Schaefer, J. Chem. Phys. 120, (2004)
3 N. Sylvetsky, K. A. Peterson, A. Karton, and J. M. L. Martin, J. Chem. Phys. 144, (2016)
4. F. Pfeiffer, G. Rauhut, D. Feller, and K.A. Peterson, J. Chem. Phys. 138, (2013)

8. VPT2 Results
CH3O2 radical has the most amount of modes assigned1,2, so direct comparisons with experiment can be made
Experimental
QZ+TZ TZ DZ
TZ+DZ
DZ+B3LYP
DZ+MP2
3030.0
3020.0
2968.0
1453.0
1440.0
1414.0
1183.0 X
1112.0
902.0
916.21
915.12
916.79
915.69
914.64
917.08
492.0
491.92
492.02
496.06
495.81
495.13
495.77 x
135.76
136.19
135.14
132.85
126.13
151.73
RMSD
5.73
5.61
6.58
5.94
6.74
9.57
1. J.Agarwal,A.Simmonett,H.Schaefer III, Molecular Physics 110, 2419(2012)
2. D.R. Huang, L.K. Chu and Y.P. Lee, J. Chem. Phys. 127, (2007)

9. CH3O2H VPT2 Results 3 modes are known (2963.8,1478.1,1320.7cm-1)1
Experimental TZ DZ
TZ+DZ
DZ+B3LYP
DZ+MP2
2963.8
1478.1
1320.7
831.07
832.81
832.07
839.73
834.88
443.97
444.05
443.81
445.97
444.45
243.82
244.11
243.30
244.70
244.48
176.76
177.23
177.39
77.74
128.52
RMSD X
2.54
1.06
26.44
14.49
1. Niki.H, Maker,P.D,Savage C.M,Breitenback,L.P Journal of Physical Chemistry 87, 2190(1983)

10. CH3O2 Anion VPT2 Results No Experimental Results TZ TZ+DZ DZ DZ+MP2
DZ+B3LYP
1463.7
1145.6
777.72
777.53
779.68
782.06
425.33
424.42
264.6
264.64
263.64
263.77
RMSD
4.16
4.67
15.60
23.70

11. CH3O2 Cation VPT2 Results No Experimental Results TZ DZ TZ+DZ DZ+MP2
DZ+B3LYP
463.91
458.50
456.28
479.49
467.32
308.76
300.77
300.08
317.52
304.58
104.33
85.62
85.59
68.85
71.39
RMSD
8.99
9.02
39.11
19.93

12. Effects Of Composite Quantities on Enthalpy
Contributions to TAE (Total Atomization Energy)
TAE
kJ/mol
% Contribution HF
CCSD
(T)
2.4997
Rel
0.0906
DBOC
0.3223
0.0157
ZPVE
5.4296
CH3O2 (2A´´)(Units in Hartrees unless explicitly stated) HF
CCSD
(T)
Relativistic
ZPVE
DBOC
Total Energy
TAE
TAE(kJ/mol)
delta H (0k,kJ/mol)
0.0426
0.0071
0.6975
21.81

13. Level Derived Quantities
∆ 𝐻 0𝐾 ,∆ 𝐻 298𝑘 in units of KJ/mol
Currently ROMP2-F12/cc-pvtz-f12 VPT2 corrections are being computed. UMP2/aug-cc-pvtz was the cause of the poor levels in previous slides.
Uncertainity assigned for similar ccsd(t)-f12b composite schemes on HEAT test suite is 0.95 kj/mol1
∆ 𝐻 𝑓,0𝐾 Enthalpies of formation (kJ/mol)
Basis
CH3O2 Cation
CH3O2
CH3O2 Anion
CH3O2H
QZ+TZ X
21.81 TZ
21.77
-91.17
TZ+DZ
-91.19 DZ
21.91
-91.04
DZ+B3LYP
21.98
-91.12
Reference
1012.2(+/-2.0)
22.29(+/- .49)
-90.23(+/-.99)
(+/-0.91)
1.J.Zhang,E.Valeev,JCTC 8,3175 (2012)
2.B. Ruscic and D. H. Bross, Active Thermochemical Tables (ATcT) values based on ver of the Thermochemical Network (2016); available at ATcT.anl.gov

14. Level Derived Quantities
Anharmonic levels were used with harmonic oscillator approximation
Uncertainty is 0.95 kJ/mol
∆ 𝐻 𝑓,298𝐾 Enthalpies of formation (kJ/mol)
Basis
CH3O2 Cation
CH3O2
CH3O2 Anion
CH3O2H
QZ+TZ x
12.41 TZ
12.36
-99.39
TZ+DZ
12.34
-99.48 DZ
12.47
-99.33
DZ+B3LYP
12.55
-99.62
Reference
1003.8(+/-2.0)
12.54(+/-0.49)
-99.94(+/-0.67)
(+/-0.74)

15. Conclusions
For spectroscopic purposes, CCSD(T)-F12b/VPT2 will give the best agreement with what experimental information is available for methyl peroxides and hydroperoxides
Accurate ZPVE’s for composite computations can be CCSD(T)-f12b/VPT2. It is possible for a large basis harmonic frequency CCSD(T)-f12b pair with VPT2 done with a smaller basis CCSD(T)-f12b computation to obtain accurate ZPVE’s

16. Acknowledgements Branko Ruscic (Argonne) Richard Dawes (MST)
Collaborators
Branko Ruscic (Argonne)
Richard Dawes (MST)
Missouri S&T Graduate Students and Postdocs
Sangeeta Sur, Phalgun Lolur, Andrew Powell, Steve Ndengué, Ernesto Quintas Sánchez