Analysis of the molecular electronic absorption spectra of shock-heated aromatic compounds

Abstract

Advantage has been taken of the rapid and homogeneous heating of a sample in a shock wave to record the electronic absorption spectra of the 'Al, + lBzu transition in benzene and the corresponding 'Al + 'B1 transition in toluene as a function of temperature over the range 700-1300 K, prior to thermal decomposition.A model for the band-shape function of electronic absorption spectra of symmetry-allowed and symmetry-forbidden transitions in the context of the Herzberg-Teller theory is proposed based upon the assumption of harmonic oscillators. For symmetry-forbidden transitions, frequency changes in the promoting modes are ignored and only the linear Herzberg-Teller terms are considered to account for the dependence of the electronic transition moment upon nuclear coordinates. Explicit attention is paid to the temperature dependence of the band-shape function and it is shown, in conjunction with a moment analysis of the band-shape function, how important molecular parameters may be deduced in favourable instances, which are determined chiefly by the inherent molecular complexity and symmetry point group of the molecule. It is shown by a moment analysis of the shock data that the induced and allowed transition moments in toluene are of comparable magnitude.

Collisional energy transfer probabilities of highly excited molecules from kinetically controlled selective ionization (KCSI). II. The collisional relaxation of toluene: P(E′,E) and moments of energy transfer for energies up to 50 000 cm−1

“…52,77,79,80 For 1 larger than 266 nm this dependence can be described by where 01 ( 1 ) and b( 1 ) are wavelength dependent fit parameters, see Table II for a summary. For the transformation of 1 ( 1 ,T) into 1 ( 1 ,͗E͘) in toluene one can use the relationship, 77…”

A Unified Description of the Electrochemical, Charge Distribution, and Spectroscopic Properties of the Special-Pair Radical Cation in Bacterial Photosynthesis

“…Calculated electronic hole-transfer average absorption energies h ν av are shown in Figure C. If the initial and final potential-energy surfaces are harmonic and the Condon , approximation of coordinate-independent transition probability holds, then this averaged frequency corresponds , to the vertical energy difference between the ground and excited states evaluated at the equilibrium geometry of the ground state, the so-called vertical excitation energy. Because of the vibronic couplings from the hole-transfer state to both the ground state and the SHOMO → HOMO state, the Condon approximation is not valid, and hence the connection between h ν av and the vertical excitation energy is blurred.…”

Absorption and fluorescence of toluene vapor at elevated temperatures

“…27 Our results can be compared to two other publications. 25,28 The work by Hippler et al focused on the S 0 -S 2 transition but additionally published absorption cross-section data at 280 nm. The agreement is within 10% for the high-temperature measurement (with an 80 K temperature difference between our measurements and the Hippler data).…”