Photoionization of Three Isomers of the C₉H₇ Radical

Abstract

Three resonance-stabilized radicals, 1-indenyl (Ind), 1-phenylpropargyl (1PPR), and 3-phenylpropargyl (3PPR), all isomers of the composition C(9)H(7), were generated by jet flash pyrolysis. Their photoionization was examined by VUV synchrotron radiation. The mass spectra show a clean and efficient radical generation when the pyrolysis is turned on. To study the photoionization, photoion yield measurements and threshold photoionization spectroscopy techniques were applied. We determined adiabatic ionization energies (IE(ad)) of 7.53 eV for Ind, 7.20 eV for 3PPR, and 7.4 eV for 1PPR. Ab initio calculations show no major change in geometry upon ionization, in agreement with ionization from a nonbonding molecular orbital. The IEs were also computed and are in agreement with the measured ones. The difference in the IE might allow a distinction of the three isomers in flames. In the indenyl spectrum, an excited a(+) (3)B(2) state of the cation was identified at 8.10 eV, which shows a low-energy vibrational progression of 61 meV. Furthermore, we have examined the dissociative photoionization of the precursors. The indenyl precursor, 1-indenyl bromide, undergoes dissociative photoionization to Ind(+). An appearance energy (AE(0K)) of 10.2 eV was obtained from fitting the experimental breakdown diagram. A binding energy of 1.8 eV can thus be determined for the C-Br bond in 1-indenyl bromide. The phenylpropargyl precursors 1PPBr (1-phenylpropargyl bromide/3-phenyl-3-bromopropyne) and 3PPBr (3-phenylpropargyl bromide/1-phenyl-3-bromopropyne) also lose a bromine atom upon dissociative photoionization. Approximate appearance energies of 9.8 eV for 3PPBr and 9.3 eV for 1PPBr have been determined.

Reactivity of the Indenyl Radical (C9H7) with Acetylene (C2H2) and Vinylacetylene (C4H4)

“…At the level of theory applied, the computed ionization energies are typically 0.05 eV to 0.15 eV lower compared to experimentally determined benchmarks . Considering these corrections, the computed AIE of 1‐indenyl of 7.40 eV agrees – after correction to 7.45 eV to 7.55 eV – exceptionally well with the experimentally determined values of 7.53 eV (Fischer et al …”

Threshold Photoelectron Spectroscopy of Cyclopropenylidene, Chlorocyclopropenylidene, and Their Deuterated Isotopomeres

“…The rather high temperature was also observed in former continuous beam studies on radicals produced by pyrolysis. 18,20,49 Interestingly, the unassigned low-energy band (9.02 eV) is more pronounced in our spectrum compared to the PES from Clauberg et al [13][14][15] When we follow the assignments of the previous work, the IE ad is 9.17 eV with an estimated error of 15 meV.…”

Photoionisation of the tropyl radical

“…Ionisation energies have been determined from vibrationally resolved photoelectron spectra for several open-shell species ranging from allyl [22] and propargyl [23] to indenyl (C 9 H 7 ) [24], cyclopropenylidene [25] and fulvenallenyl [26]. In the case of allyl [27–28] and propargyl [29] they are in excellent agreement with high-resolution laser studies.…”