Marcin Gronowski

Computational Chemistry

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Posts Tagged ‘electronic spectroscopy’

Electronic absorption and phosphorescence of cyanodiacetylene

Electronic absorption and emission spectra have been investigated for cyanodiacetylene, HC5N, an astrophysically relevant molecule. The analysis of gas-phase absorption was assisted with the parallel rare gas matrix isolation experiments and with density functional theory (DFT) predictions concerning the excited electronic states. Mid-UV systems: B1Δ←X1Σ+  (origin at 282.5 nm) and B1Σ←X1Σ+ (306.8 nm) were observed. Vibronic assignments have been facilitated by the discovery of the visible phosphorescence a3Σ+←X1Σ+ in solid Ar, Kr, and Xe. Phosphorescence excitation spectra, as well as UV absorption measurements in rare gas matrices, revealed the enhancement of A←X transitions. The vibronic structure of dispersed phosphorescence spectra supplied new data concerning the ground state bending fundamentals of matrix-isolated HC5N. The experimental singlet-triplet splitting, 2.92 eV in Ar, closely matches the value of 3.0 eV predicted by DFT.

Full text: J. Chem. Phys. 133 (2010) 074310

EVIDENCE FOR DIACETYLENE CATION AS THE CARRIER OF A DIFFUSE INTERSTELLAR BAND

High-quality spectra acquired at three different observatories point to the presence of a new diffuse interstellar band (DIB) at 5069 Å. The spectral profile of this DIB matches published laboratory measurements of the diacetylene cation A2Πu–X2Πg (0–0) low-temperature gas-phase optical absorption. HC4H+ is approximately 60–80 times less abundant than CH along the analyzed lines of sight. Only an upper limit could presently be inferred from the search for an analogous band of the triacetylene cation HC6H+, expected at 6001.1Å, which implies the HC6H+ to HC4H+ ratio of less than ∼1/3.
Full text: Astrophys. J. 714 (2010) L64