Overlapping Resonances Interference-induced Transparency: The $S_0\to S_2\mathrm{/}{S}_1$ Photoexcitation Spectrum of Pyrazine

The phenomenon of “overlapping resonances interference-induced transparency” (ORIT) is introduced and studied in detail for the $S_0\to S_2\mathrm{/}{S}_1$ photoexcitation of cold pyrazine (C${}_4$H${}_4$N${}_2$). In ORIT a molecule becomes transparent at specific wavelengths due to interferences between envelopes of spectral lines displaying overlapping resonances. An example is the $S_2\leftrightarrow S_1$ internal conversion in pyrazine where destructive interference between overlapping resonances causes the $S_0\to S_2\mathrm{/}{S}_1$ light absorption to disappear at certain wavelengths. ORIT may be of practical importance in multi-component mixtures where it would allow for the selective excitation of some molecules in preference to others. Interference induced cross section enhancement is also shown.