Accurate ab initio predictions of ionization energies and heats of formation for the 2-propyl, phenyl, and benzyl radicals (original) (raw)
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Accurate Calculations of the Electron Affinity and Ionization Potential of the Methyl Radical
The Journal of Physical Chemistry A, 1997
The electron affinity and ionization potential for the CH 3 radical have been calculated at high levels of ab initio molecular orbital theory. The best values are obtained by extrapolating CCSD(T)/aug-cc-pVxZ values where x ) D, T, Q to the complete basis set limit. Zero-point energies were calculated at the CCSD(T)/ aug-cc-pVTZ level and scaled to appropriate experimental values. The calculated values are EA(CH 3 ) ) 1.64 ( 0.3 kcal/mol as compared to the experimental value of 1.84 ( 0.69 kcal/mol and IP(CH 3 ) ) 9.837 ( 0.01 eV as compared to the experimental value of 9.843 ( 0.001 eV. The theoretical values included estimates of relativistic and core/valence correlation effects.
Journal of Electron Spectroscopy and Related Phenomena, 2000
Large-scale coupled cluster or coupled electron pair calculations have been carried out for the radicals H CCCH, CF and 2 3 2 2 CCl F, the anions SiC and Si C as well as the corresponding (N21) electron systems. Accurate equilibrium structures 2 4 2 5 are established in all cases. For the adiabatic ionization potential (IP) of CF , the calculations strongly favour the higher ad 3 experimental value (9.0560.01 eV). The photoelectron (PE) spectrum of CCl F is predicted to have a very complex 2 2 vibrational structure; IP (CCl F) is predicted to be 8.22 eV. The PE spectrum of SiC shows some excitation in the n and ad 2 4 4 2 n stretching vibrational modes and the PE spectrum of Si C is dominated by the adiabatic peak.
The journal of physical chemistry. A, 2014
The ionization energies for three resonance-stabilized radicals are determined: cyclohexadienyl, 1-phenylpropargyl, and methylcyclohexadienyl. The recommended ionization energies are, respectively, 6.820(1), 6.585(1), and 7.232(1) eV. That of cyclohexadienyl is found to be just 0.02 eV above a high level ab initio calculation [Bargholz, A.; Oswald, R.; Botschwina, P. J. Chem. Phys. 2013, 138, 014307], and that of 1-phenylpropargyl is found within the stated error of a recent experimental determination [Holzmeier, F.; Lang, M.; Hemberger, P.; Fischer, I. ChemPhysChem 2014, DOI: 10.1002/cphc.201402446]. The ionization energy of the methylcyclohexadienyl radical is consistent with the ortho isomer. Ionization energies of a range of isotopologues of cyclohexadienyl radical are given, along with their D1 ← D0 origin band positions, which indicate a blue shift of 18 cm(-1) per deuterium atom substituted. The ionization energy of cyclohexadienyl, along with the calculated bond dissociation...
Chemical Science, 2011
Mass-selective two-color resonant two-photon ionization (2C-R2PI) spectra of two resonance stabilized radicals (RSRs), 1-phenylallyl and benzylallenyl radicals, have been recorded under jetcooled conditions. These two radicals, while sharing the same radical conjugation, have unique properties. The D 0 -D 1 origin of the 1-phenylallyl radical is at 19208 cm À1 , with extensive vibronic structure extending over 2000 cm À1 above the D 1 origin. Much of this structure is assigned based on comparison with DFT and TDDFT calculations. Two-color photoionization efficiency scans reveal a sharp ionization threshold, providing a precise adiabatic ionization potential for the radical of 6.905 (2) eV. By comparison, the benzylallenyl radical has an electronic origin at 19703 cm À1 and Franck-Condon activity similar to phenylallyl. The photoionization efficiency curve shows a gradual onset with apparent threshold at $7.50(2) eV. Visible-visible holeburning was used to show that each radical exists in one isomeric form in the expansion. The CH stretch IR spectrum of each radical was taken using D 0 -resonant ion dip infrared spectroscopy (D 0 -RIDIRS) in a novel four-laser experiment. Comparison of the IR spectrum with the predictions of DFT B3LYP calculations leads to firm assignment of each radical as the trans isomer. TDDFT calculations on the excited states of benzylallenyl suggest the possibility that the excited state levels originally excited convert to an allplanar form prior to ionization. The potential role that these radicals could play in Titan's atmosphere as intermediates in formation pathways for polycyclic aromatic hydrocarbons (PAHs) is briefly discussed.
Chemical Science, 2011
Mass-selective two-color resonant two-photon ionization (2C-R2PI) spectra of two resonance stabilized radicals (RSRs), 1-phenylallyl and benzylallenyl radicals, have been recorded under jetcooled conditions. These two radicals, while sharing the same radical conjugation, have unique properties. The D 0 -D 1 origin of the 1-phenylallyl radical is at 19208 cm À1 , with extensive vibronic structure extending over 2000 cm À1 above the D 1 origin. Much of this structure is assigned based on comparison with DFT and TDDFT calculations. Two-color photoionization efficiency scans reveal a sharp ionization threshold, providing a precise adiabatic ionization potential for the radical of 6.905 (2) eV. By comparison, the benzylallenyl radical has an electronic origin at 19703 cm À1 and Franck-Condon activity similar to phenylallyl. The photoionization efficiency curve shows a gradual onset with apparent threshold at $7.50(2) eV. Visible-visible holeburning was used to show that each radical exists in one isomeric form in the expansion. The CH stretch IR spectrum of each radical was taken using D 0 -resonant ion dip infrared spectroscopy (D 0 -RIDIRS) in a novel four-laser experiment. Comparison of the IR spectrum with the predictions of DFT B3LYP calculations leads to firm assignment of each radical as the trans isomer. TDDFT calculations on the excited states of benzylallenyl suggest the possibility that the excited state levels originally excited convert to an allplanar form prior to ionization. The potential role that these radicals could play in Titan's atmosphere as intermediates in formation pathways for polycyclic aromatic hydrocarbons (PAHs) is briefly discussed.
Threshold Photoelectron Spectroscopy of the CH2I, CHI, and CI Radicals
The Journal of Physical Chemistry A
VUV photoionization of the CH n I radicals (with n = 0, 1, and 2) is investigated by means of synchrotron radiation coupled with a double imaging photoion-photoelectron coincidence spectrometer. Photoionization efficiencies and threshold photoelectron spectra (TPES) for photon energies ranging between 9.2 and 12.0 eV are reported. An adiabatic ionization energy (AIE) of 8.334 ± 0.005 eV is obtained for CH 2 I, which is in good agreement with previous results [8.333 ± 0.015 eV, Sztáray et al. J. Chem. Phys. 2017, 147, 013944], while for CI an AIE of 8.374 ± 0.005 eV is measured for the first time and a value of ∼8.8 eV is estimated for CHI. Ab initio calculations have been carried out for the ground state of the CH 2 I radical and for the ground state and excited states of the radical cation CH 2 I + , including potential energy curves along the C−I coordinate. Franck−Condon factors are calculated for transitions from the CH 2 I(X̃2B 1) ground state of the neutral radical to the ground state and excited states of the radical cation. The TPES measured for the CH 2 I radical shows several structures that correspond to the photoionization into excited states of the radical cation and are fully assigned on the basis of the calculations. The TPES obtained for the CHI is characterized by a broad structure peaking at 9.335 eV, which could be due to the photoionization from both the singlet and the triplet states and into one or more electronic states of the cation. A vibrational progression is clearly observed in the TPES for the CI radical and a frequency for the C−I stretching mode of 760 ± 60 cm −1 characterizing the CI + electronic ground state has been extracted.
Journal of computational chemistry, 2015
Open Shell organic radicals are principal species involved in many diverse areas such as combustion, photochemistry, and polymer chemistry. Computational studies of such species with an accurate method like coupled-cluster with single and double and perturbative triple (CCSD(T)) may be restricted to systems of modest size due to the steep computational scaling of the method. Herein, we assess the accuracy of extrapolated CCSD(T) energies determined using the connectivity-based hierarchy (CBH) method on medium to large sized radicals. In our method, an MP2 calculation on the target radical is coupled with CCSD(T) energies of fragments determined uniquely by our hierarchy to perform accurate extrapolations. A careful assessment is done with a robust CBH-rad49 test set comprising of 49 diverse cyclic and acyclic radicals with a variety of functional groups. We demonstrate that the extrapolation method with CBH-2 or CBH-3 is sufficient to obtain sub-kcal accuracy. ROMP2 and PMP2 calcula...
The Journal of Chemical Physics, 2012
The adiabatic ionization potential of the BaOH radical, as generated in a laser vaporizationsupersonic expansion source has been determined by laser photoionization experiments to be (4.55 ± 0.03) eV. This value supports the three lowest out of seven previous experimental estimates, the former ranging from 4.35 to 4.62 eV. The present result is compared to ab initio calculations, as performed using both quantum chemistry at different levels of theory and density functional theory, and trying several effective core potentials and their accompanying basis sets for Ba. The most satisfactory agreement is obtained for either the adiabatic or vertical ionization potentials that derive from post-Hartree-Fock [MP2 and CCSD(T)] treatments of electron correlation, along with consideration of relativistic effects and extensive basis sets for Ba, in both BaOH and BaOH +. Such conclusions extend to the results of related calculations on the Ba−OH dissociation energies of BaOH and BaOH + , which were performed to help in calibrating the present computational study. Bonding in BaOH/BaOH + , as well as possible sources of discrepancy with previous experimental determinations of the BaOH adiabatic ionization potential are discussed.