Cryogenic Photochemical Synthesis and Electronic Spectroscopy of Cyanotetracetylene

Abstract

HCN is a molecule of astrochemical interest. In this study, it was produced in cryogenic Ar and Kr matrices from UV-photolyzed diacetylene/cyanodiacetylene mixtures. Its strong phosphorescence was discovered and served for the identification of the compound. Vibrationally resolved phosphorescence excitation spectra gave insight into excited singlet electronic states. Two electronic systems were observed around 26 000-34 000 cm and 35 000-50 000 cm. Energies of the second excited singlet and the lowest triplet state were derived from analysis of these systems. Vibrational and electronic spectroscopic features were assigned with the assistance of density functional theory calculations. Some trends concerning the electronic spectroscopy of HCN family molecules are presented.

Low Temperature Synthesis and Phosphorescence of Methylcyanotriacetylene

“…As can be seen in Figure 7, a much less resolved UV absorption of HC 7 N in acetonitrile, reported in Wakabayashi et al, 43 appears in the same spectral region. The resemblance of HC 7 N and HC 9 N excitation spectra, reported by Szczepaniak et al, 39 helps in the assignment of bands. More precisely, at the low energy side, the spectra of both of HC 7 N and HC 9 N show weak features, most likely due to the ‫ܦ‬ − ܺ system, with a vibronic spacing of ~1930 cm -1 (a typical triple bond stretching frequency).…”

“…All details concerning the experimental set-up and spectroscopic instrumentation were given in a paper by Szczepaniak et al (this issue). 39 Experiments were primarily aimed at identification of the created photoproducts and characterization of their electronic transitions, by measuring dispersed phosphorescence spectra, as well as phosphorescence excitation spectra, and phosphorescence lifetime. Cyanodiacetylene was deposited in the amount either the same or twice smaller than that of propyne.…”

“…Studies on the synthesis of HC 7 N and HC 9 N in rare gas matrices suggested that the dominant path may consist in the attack of a (cyano)acetylenic radical on the other, intact precursor molecule. 37,39 Consequently, the following scheme may be at work once C 5 N • becomes available:…”

“…34,35 Our earlier studies [36][37][38] demonstrated the appearance of mono-and dicyanopolyacetylenes in cryogenic UV-stimulated processes, out of shorter H(C≡C) n CN species reacting with one another or with acetylenic-type molecules H(C≡C) m H. Such syntheses have already been shown to work for cyanodiacetylene (HC 5 N), 36,38 cyanotriacetylene (HC 7 N), 37 and cyanotetraacetylene (HC 9 N). 39 In particular, HC 7 N was detected in UV-irradiated (H 2 discharge lamp or 193 nm laser) solid Ar doped with either HC 3 N + C 4 H 2 or HC 5 N + C 2 H 2 mixture. 37 HC 7 N was also produced by electric discharges in a HC 3 N/Kr mixture, prior to the trapping onto a cold substrate.…”

Imaging electron-density fluctuations by multidimensional X-ray photon-coincidence diffraction

“…Its linear geometry allows a clear interpretation in both momentum and real space. This molecule was first detected in interstellar space (37) and has been studied both experimentally (38)(39)(40)(41)(42) and theoretically (43)(44)(45)(46)(47). We assume a single molecule oriented along x in the laboratory frame as shown in Fig.…”