On the Role of Methyl Torsional Modes in the Intersystem Crossing Dynamics of Isolated Molecules

Abstract

Rotationally resolved fluorescence excitation spectra of the 0(0)(0) bands of the S1<--S0 electronic transitions of 2- and 5-methylpyrimidine (2MP and 5MP, respectively) have been observed and assigned. Both spectra were found to contain two sets of rotational lines, one associated with the sigma=0 torsional level and the other associated with the sigma=+/-1 torsional level of the attached methyl group. Analyses of their structure using the appropriate torsion-rotation Hamiltonian yields the methyl group torsional barriers of V6''=1.56 and V6'=8.28 cm(-1) in 2MP and V6''=4.11 and V6'=58.88 cm(-1) in 5MP. Many of the lines in both spectra are fragmented by couplings with lower lying triplet states. Analyses of some of these perturbations yield approximate values of the intersystem crossing matrix elements, from which it is concluded that the sigma=+/-1 torsional levels of the S1 state are significantly more strongly coupled to the T1 state than the sigma=0 torsional levels.

Решение Обратной Задачи Для Сложного Вибронного Аналога Резонанса Ферми На Основе Плоских Вращений Якоби

“…Развитую методику можно было бы применить и к другим сложным спектрам [3][4][5][6][7][8][9][10][11][14][15][16][17]20], к сожалению, многие экспериментальные данные не представлены в численном виде.…”

“…Аналогичным образом с проявлением вибронного взаимодействия с участием нижних триплетных состояний T 1 и T 2 связаны особенности наблюдаемых при низких температурах спектров возбуждения фосфоресценции примесных центров бензальдегида в кристаллах ацетофенона [15], метилбензальдегида в кристаллах дурола [16], их дейтерированных производных, кристалла ацетофенона [17]. Спин-орбитальной и вибронной связью первого возбужденного синглетного состояния S 1 с близкими по энергии колебательно возбужденными состояниями триплетного состояния объяснены результаты измерений вращательно разрешенных спектров возбуждения флуоресценции пиразина [18,19], метил-производных пиримидина [20].…”

Analytic First-Order Derivatives of Partially Contracted N-Electron Valence State Second-Order Perturbation Theory (PC-NEVPT2)

“…The 0-0 transition energy E 0−0 is defined as the difference between the ZPVE-corrected energies: E 0−0 = (E ES + E ES ZPVE ) − (E GS + E GS ZPVE ). In this study, 2-, 4-, and 5-methylpyrimidine (MP) molecules, for which experimental data 69,70 are available, were selected, and CASSCF, NEVPT2, XMS-CASPT2, and some linear-response time-dependent DFT (TD-DFT) 71 with B3LYP, CAM-B3LYP, and LC-BLYP calculations were performed. First, the structures were optimized using the VTZ basis set, and single-point energy calculations were performed using the AVTZ basis set.…”

“…The perturbation density matrix d S,PT2 µν has been defined in Eq. (69). One also needs the similar contributions for the other seven excitation classes.…”

Analytic First-Order Derivatives of Partially Contracted N-Electron Valence State Second-Order Perturbation Theory (PC-NEVPT2)

“…. In this study, 2-, 4-, and 5-methylpyrimidine (MP) molecules, for which experimental data 69,70 are available, were selected, and CASSCF, NEVPT2, XMS-CASPT2, and some linear-response time-dependent DFT (TD-DFT) 71 with B3LYP, CAM-B3LYP, and LC-BLYP calculations were performed. First, the structures were optimized using the VTZ basis set, and single-point energy calculations were performed using the AVTZ basis set.…”