Violation of Hund's multiplicity rule in the electronically excited states of conjugated hydrocarbons

1985 ◽  
Vol 63 (7) ◽  
pp. 1572-1579 ◽  
Author(s):  
Shiro Koseki ◽  
Takeshi Nakajima ◽  
Azumao Toyota
Keyword(s):  
Triplet State ◽  
Excited States ◽  
Singlet State ◽  
Basis Set ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Electronically Excited States ◽  
Conjugated Hydrocarbons ◽  
Electronically Excited ◽  
Linear Polyenes

Violation of Hund's multiplicity rule in the electronically excited states of conjugated hydrocarbons is studied by using the Pariser–Parr–Pople type SCF MO method and the abinitio MO method with STO-3G basis set, both methods being augmented by CI-type treatments. It is shown that for symmetrical structures (D2h) of the nonalternant hydrocarbons, propalene, pentalene, and heptalene, the lowest excited singlet state is energetically lower than the corresponding triplet state. This is mainly due to the spin polarization (SP) effects. For D2h, structures of pentalene and heptalene the open-shell excited singlet state is predicted to be lower in energy than the closed-shell state, with the result that the former is really the ground state. Further, calculations made by including electron correlation effects reveal that in linear polyenes and polyacenes, the lowest excited singlet "minus" state (using Pariser's classification of the alternancy symmetry species) is lower in energy than the corresponding triplet state. The energy lowering of the singlet "minus" state in linear polyenes is due mostly to the mixing with the doubly excited configurations (mm → nn), while the considerable part of it in polyacenes is due to the SP effects.

The radiation-induced formation of excited states of aromatic hydrocarbons in benzene and cyclohexane. III. Effect of singlet state quenchers

1972 ◽  
Vol 328 (1575) ◽  
pp. 481-496 ◽  
Keyword(s):  
Triplet State ◽  
Excited States ◽  
State Formation ◽  
Aromatic Hydrocarbons ◽  
Extinction Coefficient ◽  
Singlet State ◽  
Excited Singlet State ◽  
Intersystem Crossing ◽  
Excited Singlet ◽  
Radiation Induced

The contribution to naphthalene and pyrene triplet state formation of intersystem crossing from the excited singlet state has been determined for both cyclohexane and benzene solutions using the singlet state quenchers nitromethane and xenon. In agreement with the conclusions reported in part II, intersystem crossing plays an important role; under certain conditions up to 50 % of the total triplet yield in naphthalene-cyclohexane solutions has this origin. The extinction coefficient for naphthalene triplet absorption in cyclohexane at λ max = 412.5 nm is 20 000 ± 5000 1 mol -1 cm -1 .

Photolysis of ketene. I

1968 ◽  
Vol 46 (14) ◽  
pp. 2353-2360 ◽  
Author(s):  
A. N. Strachan ◽  
D. E. Thornton
Keyword(s):  
Carbon Monoxide ◽  
Quantum Yield ◽  
Triplet State ◽  
Singlet State ◽  
Inert Gases ◽  
Inert Gas ◽  
Excited Singlet State ◽  
Intersystem Crossing ◽  
Excited Singlet ◽  
Increasing Temperature

Ketene has been photolyzed at 3660 and 3130 Å both alone and in the presence of the inert gases C4F8 and SF6. The quantum yield of carbon monoxide has been determined at both wavelengths as a function of pressure and temperature. At 3660 Å the quantum yield decreases with increasing pressure but increases with increasing temperature. At 3130 Å the quantum yield with ketene alone remains 2.0 at both 37 and 100 °C at pressures up to 250 mm. At higher pressures of ketene or with added inert gas the quantum yield decreases with increasing pressure. The results are interpreted in terms of a mechanism in which intersystem crossing from the excited singlet state to the triplet state occurs at both wavelengths, and collisional deactivation of the excited singlet state by ketene is single stage at 3660 Å but multistage at 3130 Å.

A NEW BAND SYSTEM OF THE P2 MOLECULE ANALOGOUS TO THE LYMAN–BIRGE–HOPFIELD BANDS OF N2

1958 ◽  
Vol 36 (5) ◽  
pp. 565-570 ◽  
Author(s):  
A. E. Douglas ◽  
K. Suryanarayana Rao
Keyword(s):  
Excited States ◽  
Ground State ◽  
Singlet State ◽  
Band System ◽  
Excited Singlet State ◽  
Lower State ◽  
High Dispersion ◽  
Electron Configuration ◽  
Excited Singlet ◽  
New System

Five bands of a new band system of P2 have been photographed at high dispersion and analyzed. The upper state of the system is a 1П0 state and lies lower than any previously known excited singlet state. The lower state of the new system is the ground state of P2 and the analysis of the new bands has given improved constants for this state. The new system appears to be the analogue of the Lyman–Birge–Hopfield bands of N2. The electron configuration of the low excited states of P2 and of related molecules is discussed.

The radiation-induced formation of excited states of aromatic hydrocarbons in benzene and cyclohexane, II. Yields of excited singlet and triplet state solute molecules

1972 ◽  
Vol 328 (1575) ◽  
pp. 457-479 ◽  
Keyword(s):  
Excited States ◽  
Pulse Radiolysis ◽  
Singlet State ◽  
Relative Yield ◽  
Excited Singlet State ◽  
High Yield ◽  
Triplet States ◽  
Excited Singlet ◽  
Concentration Dependences ◽  
Radiation Induced

The concentration dependences of the yield of excited triplet states, G ( 3 S*), and the concentration dependences of the relative yield of radiation-induced fluorescence obtained on pulse radiolysis of solutions of naphthalene, anthracene, pyrene and 2,5-diphenyloxazole (PPO) are reported. The yields of excited singlet state solute molecules, G ( 1 S*), formed on pulse radiolysis of naphthalene-cyclohexane and naphthalene-benzene solutions has been determined by comparing the intensity of the radiation-induced fluorescence with that obtained on photo-excitation. It is concluded that intersystem crossing (i.s.c.) from the excited singlet state is an important process in the formation of the high yield of triplet excited states of the solute. Under certain conditions this process accounts for up to 50 % of G ( 3 S*) in cyclohexane and the entire G ( 3 S*) in benzene solutions.

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