### The theoretical study of temperature- and pressure-dependent reactions kinetic for unimolecular isomerization reactions of C2H5O radical

#### Abstract

Minimum energies for the C_{2}H_{5}O radical, products and transition states of reactions on the potential energy surface were obtained at the MP2/6-311++G(3df,2pd) high level of theory, and single-point energies were refined at the CCSD(T)/6-311++G(3df,2pd) level of theory for all stationary points. Isomerization reactions of C_{2}H_{5}O radical take place via two proton migration mechanisms: C_{2}H_{5}O → CH_{3}CHOH (1,2-H shift) **(1)** and C_{2}H_{5}O → CH_{2}CH_{2}OH (1,3-H shift) **(2)**. Temperature and pressure-dependent rate constants of the two reactions **(1)** and **(2)** were calculated by using transitional state theory (TST) and Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Obtained results show that the reaction rate constants were: k_{∞}^{TST}(T)** (1)** = 1.978.10^{10}.T^{0.428 }exp(-13530.4/T), k_{∞}^{TST}(T)** (2)** = 3.077.10^{10}.T^{0.403 }exp(-14347.2/T); k_{∞}^{RRKM}(T)** (1)** = 1.664.10^{12}.T^{0.204 }exp(-15465.0/T), k_{∞}^{RRKM}(T)** (2)** = 1.183.10^{12}.T^{0.147 }exp(-15927.1/T) using TST and RRKM theory, respectively. The pressure-dependent rate constants of isomerization reactions being analysed and solved by RRKM theory and master equation (ME) method were k(T,P)** (1)** = 9.110.10^{7}.P^{0.815 }exp(-4959.3/T) and k(T,P)** (2) ** = 1.382.10^{7}.P^{0.850 }exp(-5009.5/T). Our results suggest that, rate constants of both **(1)** and **(2)** depend linearly on pressure in the low-temperature and pressure ranges, or in the high-temperature range. Conversely, rate constants of both **(1)** and **(2)** are nearly not depending on pressure in the low-temperature and high-pressure ranges.

**Keywords. **Potential energies surface, isomerization reactions, Rice-Ramsperger-Kassel-Marcus theory.