Find the transition state and calculate the barrier height (ΔV^≠) for the following reaction.

reaction：HNC → HCN
methods : MP2/aug-cc-pVTZ、MP2/6-31+G**

	(unit: Hartress)		(unit: kcal/mol)
HNC → HCN	HNC	TS	ΔV≠
MP2/6-31+G**	-93.14306	-93.08701	35.2
MP2/aug-cc-pVTZ	-93.23130	-93.17648	34.4

 

Calculate the k(rate constant) in different temperatures (at least 3 different temperatures) for the following reaction and plot of ln(k) versus 1000/T then compare with the experimental values. 

reaction：CH₄ +OH․→ H₂O + CH₃․
methods : MP2/aug-cc-pVTZ、MP2/6-31+G**

 

H
	Gibbs free Energies in MP2/aug-cc-pVTZ level						MP2/aug-cc-pVTZ
T(K)	CH4	OH	TS	ΔG‡	1000/T	VR (cm3 mol-1)	k	lnk	EXP	absolute error
100	-40.37349	-75.62215	-115.98312	7.9	10.0	8205.7	1.9E-25	-56.9	-43.9	13.0
200	-40.37966	-75.62815	-115.99246	9.6	5.0	16411.5	3.4E-18	-40.2	-35.4	4.8
300	-40.38650	-75.63473	-116.00286	11.5	3.3	24617.2	1.0E-15	-34.5	-32.6	1.9
400	-40.39380	-75.64169	-116.01406	13.4	2.5	32822.9	2.0E-14	-31.5	-31	0.5
500	-40.40148	-75.64893	-116.02595	15.3	2.0	41028.7	1.4E-13	-29.6	-29.9	-0.3
600	-40.40951	-75.65638	-116.03846	17.2	1.7	49234.4	5.5E-13	-28.2	-29	-0.8
	hartrees			kcal/mol					MAE	3.6

 

 

 

	Gibbs free Energies in MP2/6-31+G** level						MP2/6-31+G**
T(K)	CH4	OH	TS	ΔG‡	1000/T	VR (cm3 mol-1)	k	lnk	EXP	absolute error
100	-40.32489	-75.53680	-115.84422	11.0	10.0	8205.7	3.1E-32	-72.6	-43.9	28.7
200	-40.33185	-75.54280	-115.85333	13.4	5.0	16411.5	2.7E-22	-49.7	-35.4	14.3
300	-40.33948	-75.54938	-115.86350	15.9	3.3	24617.2	6.5E-19	-41.9	-32.6	9.3
400	-40.34757	-75.55634	-115.87447	18.5	2.5	32822.9	3.7E-17	-37.8	-31	6.8
500	-40.35603	-75.56358	-115.88614	21.0	2.0	41028.7	4.7E-16	-35.3	-29.9	5.4
600	-40.36483	-75.57104	-115.89841	23.5	1.7	49234.4	2.8E-15	-33.5	-29	4.5
	hartrees			kcal/mol					MAE	11.5

 

 

reaction：CD4 +OH․→ H2O(1 H will replace by D) + CD3․

methods : MP2/aug-cc-pVTZ、MP2/6-31+G**

	Gibbs free Energies in MP2/6-31+G** level						MP2/6-31+G**
T(K)	CD4	OH	TS	ΔG‡	1000/T	VR (cm3 mol-1)	k	lnk
100	-40.33766	-75.53680	-115.85518	12.1	10.0	8205.7	1.0E-34	-78.3
200	-40.34506	-75.54280	-115.86461	14.6	5.0	16411.5	1.3E-23	-52.7
300	-40.35315	-75.54938	-115.87518	17.2	3.3	24617.2	8.0E-20	-44.0
400	-40.36174	-75.55634	-115.88664	19.7	2.5	32822.9	7.6E-18	-39.4
500	-40.37079	-75.56358	-115.89888	22.3	2.0	41028.7	1.3E-16	-36.6
600	-40.38025	-75.57104	-115.91182	24.8	1.7	49234.4	9.7E-16	-34.6
	hartrees			kcal/mol

 

chatgpt

Reference

Optimization keywords

Direct measurements of the rate coefficient for the reaction OH+CH4 → CH3+H2O over 300-1500 K

Tomasz Gierczak, Ranajit K. Talukdar, Scott C. Herndon, Ghanshyam L. Vaghjiani, and A. R. Ravishankara, Rate Coefficients for the Reactions of Hydroxyl Radicals with Methane and Deuterated Methanes J. Phys. Chem. A 1997, 101, 3125-3134.

R. Atkinson, Kinetics of the gas-phase reactions of OH radicals with alkanes and cycloalkanes Atmos. Chem. Phys. 2003, 3, 2233 –2307.

Jun Li, and Hua Guo, Thermal Rate Coefficients and Kinetic Isotope Effects for the Reaction OH + CH4 → H2O + CH3 on an ab Initio-Based Potential Energy Surface J. Phys. Chem. A 2018, 122, 2645-2652.