Ionization Energies and Dyson Orbitals of Cytosine and 1-Methylcytosine

Dolgounitcheva, O.; Zakrzewski, V. G.; Ortiz, J. V.

doi:10.1021/jp021996y

Cited by 32 publications

(40 citation statements)

References 35 publications

(93 reference statements)

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“…56,62,63 Since a large geometry change is expected for the S 1 → D 0 transition, the Franck-Condon factor of the adiabatic transition in ionization is expected to be very small.…”

Section: Photoionization Efficiency Curves and Thresholdsmentioning

confidence: 99%

The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine

Trachsel

Wiedmer

Blaser

et al. 2016

The Journal of Chemical Physics

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We have investigated the S0 → S1 UV vibronic spectrum and time-resolved S1 state dynamics of jet-cooled amino-keto 1-methylcytosine (1MCyt) using two-color resonant two-photon ionization, UV/UV holeburning and depletion spectroscopies, as well as nanosecond and picosecond time-resolved pump/delayed ionization measurements. The experimental study is complemented with spin-component-scaled second-order coupled-cluster and multistate complete active space second order perturbation ab initio calculations. Above the weak electronic origin of 1MCyt at 31 852 cm−1 about 20 intense vibronic bands are observed. These are interpreted as methyl group torsional transitions coupled to out-of-plane ring vibrations, in agreement with the methyl group rotation and out-of-plane distortions upon 1ππ∗ excitation predicted by the calculations. The methyl torsion and ν1′ (butterfly) vibrations are strongly coupled, in the S1 state. The S0 → S1 vibronic spectrum breaks off at a vibrational excess energy Eexc ∼ 500 cm−1, indicating that a barrier in front of the ethylene-type S1⇝S0 conical intersection is exceeded, which is calculated to lie at Eexc = 366 cm−1. The S1⇝S0 internal conversion rate constant increases from kIC = 2 ⋅ 109 s−1 near the S1(v = 0) level to 1 ⋅ 1011 s−1 at Eexc = 516 cm−1. The 1ππ∗ state of 1MCyt also relaxes into the lower-lying triplet T1 (3ππ∗) state by intersystem crossing (ISC); the calculated spin-orbit coupling (SOC) value is 2.4 cm−1. The ISC rate constant is 10–100 times lower than kIC; it increases from kISC = 2 ⋅ 108 s−1 near S1(v = 0) to kISC = 2 ⋅ 109 s−1 at Eexc = 516 cm−1. The T1 state energy is determined from the onset of the time-delayed photoionization efficiency curve as 25 600 ± 500 cm−1. The T2 (3nπ∗) state lies >1500 cm−1 above S1(v = 0), so S1⇝T2 ISC cannot occur, despite the large SOC parameter of 10.6 cm−1. An upper limit to the adiabatic ionization energy of 1MCyt is determined as 8.41 ± 0.02 eV. Compared to cytosine, methyl substitution at N1 lowers the adiabatic ionization energy by ≥0.32 eV and leads to a much higher density of vibronic bands in the S0 → S1 spectrum. The effect of methylation on the radiationless decay to S0 and ISC to T1 is small, as shown by the similar break-off of the spectrum and the similar computed mechanisms.

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“…56,62,63 Since a large geometry change is expected for the S 1 → D 0 transition, the Franck-Condon factor of the adiabatic transition in ionization is expected to be very small.…”

Section: Photoionization Efficiency Curves and Thresholdsmentioning

confidence: 99%

The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine

Trachsel

Wiedmer

Blaser

et al. 2016

The Journal of Chemical Physics

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“…Theoretically, dedicated investigations were performed in order to predict the adiabatic ionization energies (AIE) or vertical ionization energies (VIE), and/or to assign the bands observed in the photoelectron spectra, i.e., their π or n character, for example. [18][19][20][21][22][23][24][25][26] Moreover, combined experimental and theoretical studies on ionization properties of dimers of nucleobases have been reported too. [27][28][29][30] These dimers represent models of the non-covalent interactions occurring during the DNA double strand formation or in the RNA folding.…”

Section: Introductionmentioning

confidence: 99%

VUV photoionization of gas phase adenine and cytosine: A comparison between oven and aerosol vaporization

Touboul

Gaie-Levrel

Garcı́a

et al. 2013

The Journal of Chemical Physics

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We studied the single photon ionization of gas phase adenine and cytosine by means of vacuum ultraviolet synchrotron radiation coupled to a velocity map imaging electron∕ion coincidence spectrometer. Both in-vacuum temperature-controlled oven and aerosol thermodesorption were successfully applied to promote the intact neutral biological species into the gas phase. The photoion yields are consistent with previous measurements. In addition, we deduced the threshold photoelectron spectra and the slow photoelectron spectra for both species, where the close to zero kinetic energy photoelectrons and the corresponding photoions are measured in coincidence. The photoionization close and above the ionization energies are found to occur mainly via direct processes. Both vaporization techniques lead to similar electronic spectra for the two molecules, which consist of broadbands due to the complex electronic structure of the cationic species and to the possible contribution of several neutral tautomers for cytosine prior to ionization. Accurate ionization energies are measured for adenine and cytosine at, respectively, 8.267 ± 0.005 eV and 8.66 ± 0.01 eV, and we deduce precise thermochemical data for the adenine radical cation. Finally, we performed an evaluation and a comparison of the two vaporization techniques addressing the following criteria: measurement precision, thermal fragmentation, sensitivity, and sample consumption. The aerosol thermodesorption technique appears as a promising alternative to vaporize large thermolabile biological compounds, where extended thermal decomposition or low sensitivity could be encountered when using a simple oven vaporization technique.

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“…15 More reliable values of valence-shell VIEs of the five lowest-energy tautomers obtained using electron propagator methods were reported by Ortiz and coworkers. 21 However, accurate estimates of the AIEs and valence-shell VIEs obtained at the same level of theory (so that ionization-induced relaxation effects can be quantified) for the most stable cytosine tautomers that are likely to be populated in the experiment are still missing. As discussed in Refs.…”

Section: Introductionmentioning

confidence: 99%

Ionization of cytosine monomer and dimer studied by VUV photoionization and electronic structure calculations

Kostko

Bravaya

Krylov

et al. 2010

Phys. Chem. Chem. Phys.

124

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Photoionization of the cytosine dimer 2 SummaryWe report a combined theoretical and experimental study of ionization of cytosine monomers and dimers.Gas-phase molecules are generated by thermal vaporization of cytosine followed by expansion of the vapor in a continuous supersonic jet seeded in Ar. The resulting species are investigated by single photon ionization with tunable vacuum-ultraviolet (VUV) synchrotron radiation and mass analyzed using reflectron mass spectrometry. Energy onsets for the measured photoionization efficiency (PIE) spectra are 8.60±0.05 eV and 7.6±0.1 eV for the monomer and the dimer, respectively, and provide an estimate for the adiabatic ionization energies (AIE). The first AIE and the ten lowest vertical ionization energies (VIEs) for selected isomers of cytosine dimer computed using equation-of-motion coupled-cluster (EOM-IP-CCSD) method are reported. The comparison of the computed VIEs with the derivative of the PIE spectra, suggests that multiple isomers of the cytosine dimer are present in the molecular beam. The calculations reveal that the large red shift (0.7 eV) of the first IE of the lowest-energy cytosine dimer is due to strong inter-fragment electrostatic interactions, i.e., the hole localized on one of the fragments is stabilized by the dipole moment of the other. A sharp rise in the CH + signal at 9.20±0.05 eV is ascribed to the formation of protonated cytosine by dissociation of the ionized dimers. The dominant role of this channel is supported by the computed energy thresholds for the CH + appearance and the barrierless or nearly barrierless ionization-induced proton transfer observed for five isomers of the dimer.3

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Ionization Energies and Dyson Orbitals of Cytosine and 1-Methylcytosine

Cited by 32 publications

References 35 publications

The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine

The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine

VUV photoionization of gas phase adenine and cytosine: A comparison between oven and aerosol vaporization

Ionization of cytosine monomer and dimer studied by VUV photoionization and electronic structure calculations

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