Vacuum ultraviolet spectroscopy of cyanogen and cyanoacetylenes

Abstract

The vapor phase absorption spectra of cyanogen, cyanoacetylene, dicyanoacetylene, and dicyanodiacetylene have been recorded between 2000 and 1050 Å. Substantial perturbations in the intensity and positions of particular bands upon the addition of helium at 1500 psi pressure served to identify several Rydberg series. These series are assigned on the basis of their quantum defects and symmetry considerations. CNDO/2-CI calculations were used to interpret the valence shell transitions. A very intense intravalence shell band, assigned as a Σu+1 ← 1Σg+ system arising from the lowest π→π* configuration, dominates the spectra of all the molecules. A moderately intense intravalence shell band, assigned as a Πu1 ← 1Σg+ transition arising from the lowest n→π* configuration further characterizes the spectra.

Rydberg states of cyanoacetylene investigated by (3 + 1) REMPI spectroscopy in the 77,000–90,000 cm−1 energy range

“…It was later analysed by Okabe and Dibeler [7] and by Connors et al [1]. The latter analysis revealed strong transitions to valence states superimposed on Rydberg series in the VUV region between 170 and 100 nm, i.e.…”

“…Moreover, oscillator strengths of various valence excitations were estimated in the calculations and enabled to assign the most intense valence bands observed in the absorption spectrum. Connors et al [1] also assigned the most intense Rydberg transitions to two series, R and R 0 , with weak vibrational progressions. From the measured quantum defects, they tentatively assigned the R series to an ns series and the R 0 series to an np series.…”

“…between 58,800 and 100,000 cm À1 . By varying the concentration of the neon carrier gas in their experiments, Connors et al [1] could discriminate the Rydberg bands, very sensitive to pressure effects (spectral shift and broadening), from the valence bands, less sensitive to pressure effects. In addition these authors obtained the molecular orbital energies of HC 3 N, from an SCF calculation associated to a moderate configuration interaction.…”

“…Indeed, the same series are allowed by one-photon and three-photon selection rules, with additional series allowed in the three-photon spectrum. It is therefore interesting to re-examine the previous absorption assignments of Connors et al [1] in the region of the Rydberg series above 77,000 cm À1 (below 129.9 nm) and to complete, when possible, the analysis of Ref. [1].…”

Low-temperature phosphorescence of dicyanoacetylene in rare gas solids

“…1) is a rod-shaped molecule, first synthesized by Moureu and Bongrand [1]. 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].…”