The Electronic Spectra of Unsubstituted Mono‐ to Pentaacetylene in the Gas Phase and in Solution in the Range 1100 to 4000 Å

Abstract

acetylene in the Gas Phase and in Solution in the Range 1100 to 4000Summary. The electronic spectra of the title compounds I(n), n = 1 to 5, were recorded under standard conditions for quantitative comparison. Spectra of 1(1) to 1(4) in the gas phase and of I(2) to 1(5) in nonpolar solutions are presented in a computer plotted form, and wave length maxima and intensities are listed. Tcntative assignments of the medium-intensity, first transition (A band) and the ultrahigh-intensity, second transition (B band) are given. Finally, spectra of I(2) to 1(5) rccorded at -150" are presented and discussed (A band). The syntheses of 1(3) to 1(5) are given in detail. treatment will appear in a separate paper [12].

On the Origin of Cometary C2and C3: Hydrogen Atom Migration in Diacetylene?

“…However, the rupture during the actual photolysis most likely occurs with C 10 H 2 in an electronically excited state. Moreover, the interaction between the C 10 H 2 molecules and the solvent molecules is considerable, as shown by the $20 nm redshift of the so-called B-band UV absorption spectrum of polyynes from the gas phase to n-hexane solution (Kloster-Jensen et al 1974;Eastmond et al 1972). The strength of the À2-À3 bond and the geometry of the excited molecule in solution are unknown.…”

“…The photolysis of C 10 H 2 of this study was carried out in solution, because the synthesis of C 10 H 2 in the gas phase can lead to explosions, and because the absorption spectrum of C 10 H 2 in the gas phase is unknown. However, the absorption spectra of C 6 H 2 and C 8 H 2 are known both in solution and in the gas phase (Eastmond et al 1972;Kloster-Jensen et al 1974). The absorption spectra of C 6 H 2 and C 8 H 2 in the gas phase are blueshifted by approximately 20 nm relative to the solutions.…”

Vacuum ultraviolet photochemistry of solid acetylene: a multispectral approach

“…This hampers their individual identification (Jolly & Bénilan 2008). Here, the combination of FTIR spectroscopy with UV-VIS spectroscopy provides complementary information for identifying photoproducts, since the absorption features in the UV-VIS provide better uniqueness, allowing for easier identification (Kloster-Jensen et al 1974;Grutter et al 1998). …”

“…High-performance liquid-chromatography (HPLC) analysis revealed the spectra obtained by Cataldo (2004) to be due to polyynes in the C 6 H 2 −C 16 H 2 range, although no spectroscopic assignments were made. The UV-VIS spectra of polyynes typically feature the 1 Σ + u ← 1 Σ + g as the strongest transition accompanied by multiple vibronic progressions ( Kloster-Jensen et al 1974) towards the short wavelength side. On the long wavelength side of this system, two overlapping forbidden electronic transitions ( 1 Σ − u ← 1 Σ + g and 1 Δ u ← 1 Σ + g ) and their vibronic progressions appear albeit with oscillator strengths that are three orders of magnitude smaller.…”

“…On the long wavelength side of this system, two overlapping forbidden electronic transitions ( 1 Σ − u ← 1 Σ + g and 1 Δ u ← 1 Σ + g ) and their vibronic progressions appear albeit with oscillator strengths that are three orders of magnitude smaller. When using the band assignments of liquid matrix polyynes as observed by Kloster-Jensen et al (1974) to interpret our spectra (Fig. 6), the strongest signals are likely due to C 8 H 2 , with longer polyyne signals, possibly up to C 20 H 2 , hidden in the broad wing extending up to 400 nm.…”