On large amplitude motions of simplest amides in the ground and excited electronic states

N.V Tukachev,I.A Godunov,V.A Bataev

doi:10.1051/epjconf/201713203048

Abstract

For the formamide, acetamide, N-methylformamide and N-methylacetamide molecules in the ground (S0 ) and lowest excited singlet (S1 ) and triplet (T1 ) electronic states equilibrium geometry parameters, harmonic vibrational frequencies, barriers to conformational transitions and conformer energy differences were estimated by means of MP2, CCSD(T), CASSCF, CASPT2 and MRCI ab initio methods. One-, two- and three-dimensional potential energy surface (PES) sections corresponding to different large amplitude motions (LAM) were calculated by means of MP2/aug-cc-pVTZ (S0 ) and CASPT2/cc-pVTZ (S1 ,T1 ). For these molecules, in each excited electronic state six minima were found on 2D PES sections. Using PES sections, different anharmonic vibrational problems were solved and the frequencies of large amplitude vibrations were determined.

Highlights

For the formamide, acetamide, N-methylformamide and Nmethylacetamide molecules in the ground (S0) and lowest excited singlet (S1) and triplet (T1) electronic states equilibrium geometry parameters, harmonic vibrational frequencies, barriers to conformational transitions and conformer energy differences were estimated by means of MP2, CCSD(T), CASSCF, CASPT2 and MRCI ab initio methods
The simplest amides (RCONHR') in the ground electronic state prove to be suitable in modelling the structure and properties of peptides, which are abundant in nature and play crucial role in many biochemical processes
The results presented in this paper are devoted to formamide (HCONH2), acetamide (CH3CONH2), N-methylformamide (HCONHCH3) and N-methylacetamide (CH3CONHCH3) in the ground (S0) and lowest excited singlet (S1) and triplet (T1) electronic states

Summary

Introduction

For the formamide, acetamide, N-methylformamide and Nmethylacetamide molecules in the ground (S0) and lowest excited singlet (S1) and triplet (T1) electronic states equilibrium geometry parameters, harmonic vibrational frequencies, barriers to conformational transitions and conformer energy differences were estimated by means of MP2, CCSD(T), CASSCF, CASPT2 and MRCI ab initio methods. The investigation of the amides in the lowest excited electronic states is important considering different photophysical and photochemical processes in which amides take part. The describing of the structure and conformational dynamics of the amide molecules in different electronic states is an important and actual problem.

Results

Conclusion