Knowledge Bank

Transient absorption spectra of $C2H$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C2H$ in the region 3250 to $3600cm-1$ have been obtained using ArF excimer laser flash photolysis of acetylene and color center laser probing 0.6 usec after the flash. The principal aim of the work was to observe and identify the CH stretching fundamental. Therefore, approximately 20 Torr of H2 was added to provide efficient relaxation of the $C2H$ produced to the ground vibrational state. For the color center probe beam a 2 meter long multiple reflection (White) cell was configured so as to overlap the photolysis region of the excimer. IR path lengths of 40 meters were typical. Several new bands of $C2H$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C2H$ have been observed and fitted. Bands originating from both the ground state and excited vibrational states were observed for both species. These Include three $C2H$ bands of $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma +-2\Sigma +$ symmetry. three $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C2H$ bands of $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma +-2\Sigma +$ symmetry, and one $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C2H$ band of $2\Pi +-2\Sigma +$ symmetry. Three of the $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C2H$ bands have been assigned as analogues of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C2H$ bands observed here and in previous works. The assignment of the CH stretch is still uncertain, however two of the three $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma +-2\Sigma +$ ground state $C2H$ bands are possible candidates.