Theoretical Studies On The Photodissociation Process In Excited States Of Acetone

The ketone has abundant and typical chemistry properties, so it has been concerned by people. As acetone is the simplest ketone, people regard it as a model for a large number of experimental studies of photochemical reaction. Many theoretical literatures have studied the photochemical reaction of acetone, but theoretical studies on excited state dissociation mechanism of acetone are not comprehensive. In addition, some of the previous calculation of the excited state of research in molecular dissociation reaction accuracy is not enough, indicating that the mechanism is not accurate enough. In this paper, more comprehensive analysis on the dissociation process in excited states of acetone.Firstly, The structure of the configuration optimization and frequency analysis on the ground state and the lowest triplet excited state of acetone molecular are calculated by using the B3LYP/6-31G(d, p) method. Ultimately determine their stability geometry constructions, and use TS method search for a transitional state, by the intrinsic reaction coordinate IRC calculate and prove it is correct. On this basis, theoretical analysis on the Norrish-I type dissociation reaction channel in the triplet excited state of acetone. Acetone's ground state (So) to Si, then go to triplet excited state (Ti) by photon absorption, then the triplet excited state to transition state, Finally, generate product CH3CO+CH3:After that, using ab-initio quantum chemical method to study the ground state and the excited state dissociation to CH3COCH3->CH3CCH3+O process of acetone molecules' Cs and C2V structure. Compute dissociation curve in ground state of the acetone (CH3COCH3) dissociation to CH3CCH3 molecule and O atom in Cs symmetry by using multi-configuration self-consistent field (MCSCF) method. Construct dissociation limit of acetone and calculate the vertical excitation energy of three 1A' states, three 1A" states, six 3A' states and six 3A" states in Cs symmetry. The results tell us: Calculate the vertical excitation energy of the low-lying excited states (valence) accord with the experimental values very well by MCSCF. But the Rydberg state's results are not good. Studyπ-π* of 1A1 state in C2V symmetry by MR-MP2: In Frank-Condon, 31 A1 state and 41 A1 state appeared to avoid overlapping in 1.315 A ofC = O bond length; 21 A1 state and 31Ai state appeared to avoid overlapping in 1.365 A of C - O bond length. Soπ-π* transition of 41 A1 state in avoid cross-point transition to 3' A1 state and then transition to 21 A1 state. Use the same method to calculate the vertical excitation energy of 1A1 (l-4), 1A2(1-4), 'BK1-4), 'B2(l-4), 3A,(l-4), 3A2(l-4), 3B,(l-4), 3B2(l-4).Finally, by different basis sets of TDDFT and CIS to calculate former 20 excited states' vertical excitation energy of the acetone single state. Compare to the experimental values: It was found that the use of TDDFT/ b3p86, C and H atoms using 6-31++G** basis set, O atoms use d-aug-cc-pvtz basis set with diffuse, calculation of the vertical excitation energy accord with experimental values very well. And use this basis set of B3p86 method directly calculate the vertical excitation energy and vibration intensity former 20 excited states of acetone triplet state. On this basis scan the potential energy surface of C=O bond dissociation, gain potential energy curve of six 'Ai states, four 1A2 states, four 1B2 states, four 3A2 states, four 3A2 states and four 3B2 states. We find C=O dissociation reaction is difficult. And scan thej?otential energy surface of C-C bond dissociation, gain potential energy curve of five 1A' states, five 1A" states, five 3A' states and five 3A" states. As potential energy surface has repulsion state, low electronic state transition to repulsion state by vibration excite or inner-conversion, occur predissociation.