Analysis of the Near Ultraviolet Electronic Transition of Benzene

Abstract

The absorption spectrum of benzene at 2800–2200A has been analyzed. The vibrational structure of the system has been found to be in agreement with the selection rules for a forbidden transition (1A1g→1B2u). The transition becomes possible when vibrations of type Eg+ distort the molecule. Only carbon frequencies have been found to be effective. The interpreted data are collected in series on page 211. The analysis is corroborated by comparison with the absorption of solid benzene at —259°C, with the absorption spectrum of heavy benzene and with the fluorescence spectra of both benzenes.

VUV absorbing vapours in n-perfluorocarbons

“…The absorption spectrum is plotted in figure 5 (a). Our measurement is well described by previously published data in [20], [21] and [22] apart from in the small wavelength range between 163 to 175 nm. We will use our measurement throughout this paper.…”

“…Figure 5: (a) is the photon absorption coefficient for C 6 H 6 . + is our measurement and the solid line is data replotted from reference [20], [21] and [22]. (b) is the photon absorption coefficient for C 2 H 2 .…”

“…The finding of a possible admixture of benzene to the gas is very promising as this molecule has a number of well defined absorption lines in the wavelength range from 240 to 270 nm. There is a progression of absorption lines with a spacing of 160 cm −1 which can be interpreted as n − n transition of the E + u C vibration [21]. To investigate this possibility, raw C 4 F 10 gas was passed through activated carbon until the carbon was fully saturated.…”

Ultraviolet absorption spectra of seven substituted benzenes

“…The analysis of the ultraviolet absorption spectrum of benzene [10] has shown th e vibrational s tructure to b e in agreement with the selection rules for the forbidden electronic transition AI g~ B 2u • It is held tha t this transition is r ender ed possible through the distortion of the benzen e molecule by E; vibrations. Each of th e eigh t absorption bands (see fig.…”

Some Effects of Intramolecular Vibrational Energy Transfer in Complex Fluorescent Molecules

“…Since totally symmetric vibratioils lead to the simultaneous rupture of more than one bond if excited sufficiently, it is concluded that ilormal dissociation into two fragments is brought about by non-totally symmetric vibrations, the ground state energy of which is preserved during the electronic transition (25). If a forbidden transition to the fluorescent state is observed owing to the excitation of a non-totally symmetric vibration a s in benzene (26) and naphthalene (24), this vibration is rarely excited sufficiently to cause direct dissociation. Thus the normal photodissociation of polyatomic molecules involves an internal transfer of energy from totally symmetric t o non-totally symmetric vibrations.…”