Knowledge Bank

Multiple photon absorption and photodissociation using 193 nm pulsed lasers opens up a new region of the spectrum to photochemists and spectroscopists. One, two, and three photon absorption processes allow one to excite molecules in the vacuum UV at 6.4, 12.8, and 19.2 eV. The high power and efficiency of the ArF laser make it relatively easy to study excited state spectroscopy, branching ratios, internal energy distributions, and secondary reaction processes of highly energetic fragments under near collision free conditions. The photodissociation mechanisms and fragment excited state spectroscopy of several molecular systems have been the recent subjects of study in our laboratory. As an example, 193 nm photolysis of acetylene gives: $C2H$ by a one photon absorption process; $CH(A\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Delta ),CH(X2\Pi )$, and $C2(A1\Pi \nu \prime =0-5)$ fragments by two photon absorption; $C2(d3\Pi gv\prime =0-5)$ by a three photon process; and $C2C1\Pi g$ fragments by a multiphoton absorption. These fragments are characterized by fluorescence emission spectroscopy. The production mechanisms and spectroscopy of this and other interesting systems will be discussed.