Bazı Gaz Reaksiyonlarının İçsel Reaksiyon Koordinat (IRC) Hesaplamaları ile Entalpileri ve Aktivasyon Enerjileri

Abstract

Bu çalışmada bazı gaz reaksiyonlarının İçsel Reaksiyon Koordinat (IRC) hesaplamaları ile entalpileri ve aktivasyon enerjileri teorik olarak elde edildi. İlk kez olarak IRC hesaplamalarında kullanılan yaklaşık geçiş halleri, reaksiyon aşamalarını takip eden iki boyutlu Potansiyel Enerji Yüzey (PES) taramalarındaki merdiven noktalar olarak kullanıldı. Bütün hesaplamalarda, 6-31 G(d,p) seviyede Yoğunluk Fonksiyonel Teori (DFT/B3LYP) kullanıldı. Reaksiyonların PES grafiklerindeki merdiven noktalar, IRC hesaplamalarında uygun reaksiyon eğrisi bulununcaya kadar birer birer yaklaşık Geçiş Hali (TS) olarak alındı. IRC hesaplamaları ile elde edilen TS’ler tek bir negatif (imejiner) frekans için test edildi. Bütün reaksiyonların, reaktant, ürün ve geçiş hallerini gösteren enerji diyagram şemaları çizildi ve onların entalpileri ve aktivasyon enerjileri elde edildi. Entalpi değerlerinden reaksiyonların, endotermik veya ekzotermik olduğu tespit edildi. Hesaplanan aktivasyon enerjileri literatürdeki değerlerle karşılaştırıldı.

Keywords

• Gas reaksiyonu
• Entalpi
• Aktivasyon enerjisi
• IRC
• DFT

Enthalpies and Activation Energies of Several Gas Reactions by Intrinsic Reaction Coordinate (IRC) Calculations

Abstract

In the present study, we have theoretically obtained the enthalpies and activation energies of several gas reactions by Intrinsic Reaction Coordinate (IRC) calculations. Being a first time, the approximate transition states used in the IRC calculations were obtained from the saddle points on the two dimensional Potential Energy Surface (PES) scans trucking the pathway of the reactions. In all the calculations, the Density Functional Theory (DFT/B3LYP) with 6-31 G (d, p) level was used. The saddle points on the PES graphs of the reactions were used one by one as an approximate transition state (TS) in the IRC calculations until the appropriate reaction path was obtained. The obtained TS’s from the IRC calculations were tested for having only one imaginary frequency. The energy diagram schemes showing the reactants, products and transition states of all the reactions were drawn, and their enthalpies and activation energies were determined. From the enthalpy values it was decided whether the reactions are endothermic or exothermic. The calculated activation energies were compared with the ones in the literature.

Keywords

• Gas reaction
• Enthalpy
• Activation energy
• IRC
• DFT

References

1. Lefebvre A. H., Ballal D. R., “Gas Turbine Combustion: Alternative Fuels and Emissions (third ed.)”, CRC Press, Boca Raton, (2010).
2. Kroupnov A. A., Pogosbekian M. Ju., “DFT calculation-based study of the mechanism for CO2 formation in the interaction of CO and NO2 molecules”, Chem. Phys. Lett., 2018, 710, 90-95.
3. Jaroszynska-Wolinska J., “The reaction mechanism of ozone with the NO and NO2 oxides”, J. Mol. Struct.Theochem, 2010, 952, 74-83.
4. Frisch M.J., et. al., Gaussian 09 Revision D.01, Gaussian Inc, Pittsburgh PA, (2009).
5. Frisch A., Nielsen A.B., Holder A.J., Gauss View User Manual, Gaussian Inc., Pittsburg PA, (2001).
6. Wang Y., Fu G., Zhang Y., Xu X., Wan H., “O-atom transfer reaction from N2O to CO: A theoretical investigation”,Chem. Phys. Lett., 2009, 475, 202-207.
7. Tiana D., Zenga C., Wanga H., Chenga X., Zhenga Y., Xiangd C., Lia K., Zhu X., “Effect of transition metal Fe adsorption on CeO2(110) surface in themethane activation and oxygen vacancy formation: a densityfunctional theory study”, Appl. Surf. Sci., 2017, 416, 547-564.
8. Hohenberg P., Kohn W., “Inhomogeneous electron gas”, Phys. Rev., 1964, 136, b864-b871.

9. Kohn W., Sham L.J., “Self-consistent equations including exchange and correlation Effects”, Phys. Rev., 1965, 140, a1133–a1138.
10. Becke A.D., “Density-functional exchange-energy approximation with correct asymptotic behavior”, Phys. Rev. A.,1988, 38, 3098-3100.
11. Lee C., Yang W., Parr R.G., “Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density”, Phys. Rev. B.,1988, 37, 785-789.
12. Frisch M.J., et. al., Gaussian 03 Revision A.1, Gaussian Inc, Pittsburgh PA, (2003).
13. Peng C., Schlegel H. B., “Combining synchronous transit and Quasi-Newton methods for finding transition states”, Israel J. Chem.,1993, 33, 449-454.
14. Baulch D., et al.,“Evaluated kinetic and photochemical data for atmospheric chemistry: supplement I CODATA task group on chemical kinetics”, Suppl. Int. J. Phys. Chem. Ref. Data,1982, 11, 327-496.