Infrared spectral evidence of N≡C–C≡C–N≡C: Photoisomerization of N≡C–C≡C–C≡N in an argon matrix

Abstract

Ultraviolet (UV) laser photolysis of dicyanoacetylene, N≡C–C≡C–C≡N, isolated in an argon matrix at 16 K produces the iso-nitrile, N≡C–C≡C–N≡C, in sufficient concentration for direct Fourier-transform-infrared measurements of all five stretching vibrational fundamentals. The assignments for ν1 (2287.1 cm−1), ν2 (2203.6 cm−1), ν3 (2044.8 cm−1), ν4 (1202.3 cm−1), and ν5 (610.1 cm−1) are supported by a normal coordinate analysis using 20 vibrational frequencies from 7 isotopomers and by ab initio results of Botschwina et al. The di-isonitrile C≡N–C≡C–N≡C is also produced in small amounts and its infrared-active asymmetric stretches assigned as ν4 (2114.9 cm−1) and ν5 (1287.5 cm−1). As isotopic vibrational frequencies for N≡C–C≡C–C≡N were measured for the first time, the disputed assignments for the three totally symmetric stretching vibrations were re-examined through a normal coordinate analysis. Laser-induced fluorescence measured by a Fourier-transform-spectrometer during photolysis reveals the 1Σg+←3Σu+ electronic transition in dicyanoacetylene at T00=25 607 cm−1 and four vibronic transitions involving two totally symmetric stretching states of the ground electronic state.

Low-temperature phosphorescence of dicyanoacetylene in rare gas solids

“…This general spectral pattern, resembling the one observed for related linear cyanides NC 2 N, NC 6 N or HC 5 N (see Introduction), suggests a linear emitting state, 3 . the spectrum is by far dissimilar to that reported by Vuitton et al [15] ( 0) band of the progression consists of a single strong component, the second one is doubled due to the n 1 /2n 5 anharmonic interaction -as discovered in the gas-phase Raman spectrum by Miller and Hannan [3], and further studied in solid Ar by Smith et al [9]. The third group of strong bands consists of as many as three components, for which the possible explanation involves a resonance between two overtone modes and a combination mode, namely 2n 1 , 4n 5 , and n 1 + 2n 5 .…”

“…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).…”

“…Such emission, on the other hand, is not occurring for HC 3 N (cyanoacetylene). The study presented here has been carried out with the goal of revisiting the topic investigated by Smith et al [9], by giving a detailed account of NC 4 N phosphorescence in solid rare gases. Smith et al limited their description to the most intense vibronic bands (0-0, and 3 elements of the ν 1 " progression) in Ar.…”

Photochemical activity of Titan’s low-altitude condensed haze

“…The broad continuum absorption at longer wavelengths than B350 nm could be due to the weak singlet-triplet absorption amplified in the condensed phase, in agreement with detection of phosphorescence from the first triplet (T 1 ) state of C 4 N 2 at B390 nm (ref. 40).…”

Cyanoisocyanoacetylene, N≡C−C≡C−N≡C

“…Fehlhammer and Kunz [5] synthesized the alkynyl isocyanides as ligands on the metal complex fragment [(CO) 5 Cr(CNÀCCÀR)] (R H, SiMe 3 , C 6 H 5 ). Ethynyl isocyanide (R H) is the parent compound of the isocyanopolyynes, the isomers of cyanopolyynes that have been intensively studied by Kroto and et al [6] The simplest cyanoisocyanopolyyne, CNÀ(CC) n ÀCN (n 1), was obtained photochemically in an argon matrix at 16 K, and identified by IR spectroscopy [7] by comparison with the results from ab initio calculations. [8] However, a synthesis that would yield sufficient material for the measurement of rotation and high-resolution IR spectra was hitherto unavailable.…”