Ionization photophysics and Rydberg spectroscopy of diacetylene

• Published in: Molecular physics Vol. 110; no. 21-22; pp. 2843 - 2856
• Main Authors: Schwell, Martin, Bénilan, Yves, Fray, Nicolas, Gazeau, Marie-Claire, Es-Sebbar, Et, Gaie-Levrel, François, Champion, Norbert, Leach, Sydney
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Group 01-11-2012; Taylor & Francis Ltd; Taylor & Francis
• Subjects: Analytical chemistry; Sciences of the Universe; Spectrum analysis
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268976.2012.704084

Photoionization of diacetylene was studied using synchrotron radiation over the range 8-24 eV, with photoelectron-photoion coincidence (PEPICO) and threshold photoelectron-photoion coincidence (TPEPICO) techniques. Mass spectra, ion yields, total and partial ionization cross-sections were measured. The adiabatic ionization energy of diacetylene was determined as IE
ad
 = (10.17 ± 0.01) eV, and the appearance energy of the principal fragment ion C
4
H
+
as AE = (16.15 ± 0.03) eV. Calculated appearance energies of other fragment ions were used to infer aspects of dissociation pathways forming the weaker fragment ions
, C
3
H
+
,
and C
2
H
+
. Structured autoionization features observed in the PEPICO spectrum of diacetylene in the 11-13 eV region were assigned to vibrational components of three new Rydberg series, R1(nsσ
g
, n = 4-11), R2(ndσ
g
, n = 4-7) and R3(ndδ
g
, n = 4-6) converging to the A
2
Π
u
state of the cation, and to a new series R′1(nsσ
g
, n = 3) converging to the
state of the cation. The autoionization mechanisms and their consistence with specific selection rules are discussed.