Electronic absorption and phosphorescence of cyanodiacetylene

Abstract

Electronic absorption and emission spectra have been investigated for cyanodiacetylene, HC(5)N, 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 B (1)Delta<--X (1)Sigma(+) (origin at 282.5 nm) and A (1)Sigma(-)<--X (1)Sigma(+) (306.8 nm) were observed. Vibronic assignments have been facilitated by the discovery of the visible phosphorescence a (3)Sigma(+)<--X (1)Sigma(+) 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 HC(5)N. The experimental singlet-triplet splitting, 2.92 eV in Ar, closely matches the value of 3.0 eV predicted by DFT.

Simulation of Titan’s atmospheric photochemistry

“…The solid infrared bands are usually more intense than for molecules trapped in argon matrix, which facilitated the detection of combinations modes and overtones. Some of these infrared bands are assigned by comparison with the gaseous spectrum and previous experiments (Benilan et al 2007;Coupeaud et al 2008;Turowski et al 2010). The other ones are tentatively assigned in this paper (Table 2).…”

“…The cyanodiacetylene is known to absorb in the near ultraviolet at 353 nm (Fisher & Ross 2003). From the phosphorescence measurements, the lowest triplet state (T 1 ) of HC 5 N is located at ∼424 nm and we expect (vide infra) singlet-triplet absorption at >300 nm to be amplified due to solid-state effect (Gudipati 1994;Turowski et al 2010). We have not found to date any report of the photochemical formation of HC 5 N polymer, and our study reported here is the first observation of such polymerization under simulated Titan's lower atmospheric conditions.…”

Low-temperature phosphorescence of dicyanoacetylene in rare gas solids

“…The main vibronic progressions concern the mutually similar vibrations n 1 o f N C 4 N and n 2 of HC 5 N [10].…”

“…Its IR and Raman vibrational spectroscopy was thoroughly studied [2][3][4][5], as were the mid-UV [6,7] and vacuum-UV [8] electronic transitions. Electronic luminescence (phosphorescence) has so far been found for several cyanoacetylene-family molecules dispersed in solid rare-gas matrices, namely for NC 4 N [9] and HC 5 N (cyanodiacetylene) [10], for another isoelectronic pair: NC 2 N (cyanogen) [11] and C 3 N -(cyanoacetylide anion) [12], and finally for NC 6 N [13]. Such emission, on the other hand, is not occurring for HC 3 N (cyanoacetylene).…”

“…Smith et al limited their description to the most intense vibronic bands (0-0, and 3 elements of the ν 1 " progression) in Ar. We were also interested in comparing the NC 4 N phosphorescence to that of HC 5 N, recently measured by Turowski et al [10] in Ar, Kr, and Xe.…”