Rovibrational spectroscopy and intramolecular dynamics of 1,2-trans- d2 -ethene in the first CH stretch overtone region

The first overtone region of the CH stretching vibration of 1,2-trans- d2 -ethene (HDCCDH) was monitored via jet-cooled action spectroscopy and room temperature photoacoustic spectroscopy. The spectra include a strong band, which we assigned as the 1 + 9 CH stretch vibration, and five additional bands related to transitions to coupled states. The spectral features were modeled in terms of a six-state deperturbation analysis, revealing the energies of the zero-order states and the relatively strong couplings between the initially excited 1 + 9 state and the doorway states. Considering these energies and the fundamental frequencies of 1,2-trans- d2 -ethene and presuming that only low-order resonances are involved in the couplings enabled the assignment of the states. The analysis also allowed obtaining insight on energy flow and to find out that the energy oscillations between the CH stretch state and the doorway states occur on a subpicosecond time scale.