Knowledge Bank

Discrete vibronic bands of $B \mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\pi (ou\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>})⟵X \mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma g+$ transition in the $Br2$ vapour imbedded on an underlying continuum primarily due to $lo\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi lc ⟵X \mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma g+$ transition have been recorded photoacoustically in the frequency region $17740-19680cm-1$. The relative photoacoustic intensities of the bands have been used in estimating the non-radiative de-excitation cates from the upper vibronic levels. It is found that the non-radiative relaxation rate increases with the increasing vibrational quantum number of the $B \mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi (ou\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>})$ state. The relative intensities of the underlying continuum has been interpreted in terms of dissociation from the repulsive state and also from the dissociation of the $B \mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi (ou\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>})$ state. The analysis leads to relative contributions of different mechanisms of non-radiative relaxation in the region of dissociation limit of the $B \mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi (ou\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>})⟵X \mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma g+$ transition viz., dissociation from the excited vibrational level of $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi (ou\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>})$ state, energy transfer from the $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi (ou\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>})$ to the state, direct excitation to the state and non-radiative relaxation from the vibronic level of $B \mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi (ou\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>})$ state.