Mass spectra of the 2,4-pentadiynylidyne (C5H; X2Π) and 2,4-pentadiynyl-1 (n-C5H3; X2B1) radicals

We employed the crossed molecular beams method to synthesize the 2,4-pentadiynylidyne, C5H (X2Π), and the 2,4-pentadiynyl-1, n-C5H3(X2B1), radicals in situ under single collision conditions via the reactions of tricarbon molecules with acetylene and ethylene, respectively. Time-of-flight spectra of the radicals were recorded at the center-of-mass angles at various mass-to-charge ratios from m/z = 63 (C5H3+) to m/z = 36 (C3+). Integrating these time-of-flight spectra and normalizing them to the most intense peak, intensity ratios of I(m/z = 61):I(m/z = 60):I(m/z = 49):I(m/z = 48):I(m/z = 37):I(m/z = 36) = 0.49 ± 0.04:0.27 ± 0.03:1:0.15 ± 0.02:0.32 ± 0.03:0.11 ± 0.04 can be extracted for the 2,4-pentadiynylidyne radical. In case of the 2,4-pentadiynyl-1 molecule, we find intensity ratios of I(m/z = 63):I(m/z = 62):I(m/z = 61):I(m/z = 60):I(m/z = 51):I(m/z = 50):I(m/z = 49):I(m/z = 48):I(m/z = 39):I(m/z = 38):I(m/z = 37):I(m/z = 36) = 0.39 ± 0.04:0.50 ± 0.05:0.32 ± 0.03:0.10 ± 0.03:0.03 ± 0.01:1.0:0.24 ± 0.02:0.02 ± 0.01:0.24 ± 0.03:0.65 ± 0.05:0.57 ± 0.05:0.36 ± 0.03 at an electron impact energy of 70 eV. The absolute ionization cross sections of the 2,4-pentadiynylidyne and 2,4-pentadiynyl radicals were estimated to be 8.6 ± 1.7 × 10−16 cm2 and 9.7 ± 1.9 × 10−16 cm2, respectively. Our data can be employed in future space missions to detect the C5H and C5H3 radicals – crucial reaction intermediates in the formation of polycyclic aromatic hydrocarbon molecules – in the atmospheres of hydrocarbon rich planets (Jupiter, Saturn, Uranus, Neptune, Pluto) and their moons (Titan) and also in combustion flames via mass spectrometry coupled with matrix interval arithmetic.