Photophysics of low lying electronic states of Cl₂ in rare gas solids

Chlorine emission in solid rare gases was studied. The molecules excited into either the BO_u⁺ or into the ¹Π ₁ state continuum undergo a fast radiationless transition and vibrational relaxation and emit from the v=0 level of a new low lying electronic state. This new state with vibrational spacing ω_e≅280 cm^-1 is located 650 cm^-1 below the B ³Π (O_u⁺) and shows a long lifetime of 76 ms in argon. We present arguments for assigning the emission to the ³Π(2u) spin-orbit component. The cage effect on photodissociation and the B state excitation spectrum were also investigated. It is shown that the transition between the bound and continuous absorption region is gradual for guest molecules in solids, unlike the gas phase. While the low vibrational levels show only sharp zero phonon lines, the higher levels broaden and develop intense phonon wings due to increased coupling with the lattice and finally merge smoothly into the continuum.