Fragmentation of Valence and Carbon Core Excited and Ionized

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A: Kinetics, Dynamics, Photochemistry, and Excited States

Fragmentation of Valence and Carbon Core Excited and Ionized CHFCF Molecule 2

3

Viviane Morcelle, Aline Medina, Leonardo C. Ribeiro, Italo Prazeres, Ricardo R. T. Marinho, Manuela Souza Arruda, Luiz Antonio Vieira Mendes, Mabele Santos, Bruno Nunes Cabral Tenorio, Alexandre Braga Rocha, and Antonio C. F. Santos J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.8b09173 • Publication Date (Web): 06 Dec 2018 Downloaded from http://pubs.acs.org on December 7, 2018

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The Journal of Physical Chemistry

Fragmentation of Valence and Carbon Core Excited and Ionized CH2FCF3 Molecule V. Morcelle1,2 , A. Medina1, L. C. Ribeiro3, I. Prazeres1, R. R. T. Marinho3, M. S. Arruda3 , L. A. V. Mendes3, M. J. Santos4, B. N. C. Tenório5, A.B. Rocha5, A. C. F. Santos1* 1Instituto

de Física, Universidade Federal do Rio de Janeiro - 21941-972 Rio de Janeiro, RJ, Brazil

2Departamento 3Instituto 4Instituto

de Física, Universidade Federal Rural do Rio de Janeiro - 23890-000 RJ, Brazil de Física, Universidade Federal da Bahia-40210-340 Salvador, BA, Brazil

Federal de Educação, Ciência e Tecnologia do Sertão de Pernambuco, 56200-000 Ouricuri, PE, Brazil

5Instituto

de Química, Universidade Federal do Rio de Janeiro- 21941-909 Rio de Janeiro, RJ, Brazil *Corresponding

author: [email protected]

Abstract

The photofragmentation dynamics of 1,1,1,2-tetrafluoroethane (R134a) with photon energies from 12 eV up to 320 eV, surrounding the C 1s edge is discussed. The ionic moieties were measured in coincidence with the ejected electrons (PEPICO mode), and detected as a function of the photon energy. Around the C K core edge, the fragmentation profiles are examined regarding the site specific excitation of the CH2FCF3 molecule. In the present case, site-selectivity is favored by the distinct chemical environments surrounding both C atoms. NEXAFS spectrum at the C 1s edge simulation has been obtained at the TDDFT level and excited state geometry optimization calculations have been performed at the inner-shell multiconfigurational self-consistent field level. Our observations indicate that the C(H2F) 1s excitation to a highly repulsive potential expels a fluorine atom leaving the heavier radical fragment C2F3H2* which relaxes to the fundamental state of the ion C2F3H2+. On the other hand, the excitation from the C(F3) 1s carbon to a repulsive state in the C-C bond, leads to a C-C bond cleavage, explaining the observed site specific fragmentation. I-Introduction The CH2FCF3 molecule (also known as R134a or HFC-134a) has replaced the chlorofluorocarbons (CFCs) in several technological applications. The stability of CFCs, mainly due to chlorine presence, has associated them to depletion of the Earth’s ozone layer1. As a consequence, the production of CFCs has ceased and environmentally adequate alternatives were introduced, such as CH2FCF3. Since it does not contain chlorine, CH2FCF3 has zero ozone depletion potential (ODP). On the other hand, the global warming potential (GWP) of CH2FCF3 is 13002. GWP represents the relative rise toward the Earth of the infrared radiation flux owed to the presence of greenhouse gases. The atmospheric lifetime of CH2FCF3 is 13.8 years, lower than the corresponding lifetimes of CFCs and hydrochlorofluorocarbons (HCFCs). This is due to the fact that CH2FCF3 contains two C–H bonds, which

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are vulnerable to react with OH radicals, giving rise to smaller atmospheric lifetimes in Earth’s troposphere. Direct outer or inner-valence photoionization or core-level excitation of molecules constitutes alluring means for the investigation of the fragmentation dynamics. With respect to core-level investigation, the tunability of the photon energy enables to excite specific resonances neighbouring a selected inner-shell edge, supporting selective fragmentation3-6. In molecules, inner shells are strongly localized on a particular atomic component3-6. This is the reason why they are usually characterized by adopting atomic labels. The chemical environment of the core vacancies might influence the mass spectra of the photofragments, a phenomenon that is known as site-selective or site-specific photochemistry. This study is of great importance for the investigation of molecular properties, and might be useful to regulate chemical reactions. Photochemistry has been broadly studied applying initial resonant core-electron excitation in atoms of distinct elements7-9, in the so-called element-specific photofragmentation, and on atoms of the same element though in a distinct chemical environment7-9, which is known as site-specific photofragmentation. In other words, fragmentation of molecules after inner-shell ionization or excitation can be either specific or unspecific in regarding to the chemical environment of the ionization site. This verdict is usually interpreted in terms of an (or lack of) equilibration of internal energy into vibrational degrees of freedom8, where the core ionization or excitation of the same species but chemically different atoms can be recognized by their chemical shifts. Zhou, Seccombe, and Tuckett10 measured the threshold photoelectron and TPEPICO spectra of CF3–CH2F and CHF2–CHF2 over the energy range between 12 eV and 25 eV. They showed that decay from the first and second excited states of CF3– CH2F+ takes place impulsively by C–F bond breaking to CF2– CH2F+ (or CF3–CH2+) + F, with a large fraction of the available energy, channeled into translational energy of the products. The ground and higher-lying states of both CF3–CH2F+ dissociate by C–C bond fission to CH2F+ + CF3 and CF3+ + CH2F. This paper deals with valence, C 1s ionization, and selective excitation of the resonances of CH2FCF3 molecule.The issues addressed in this paper are: i) to investigate the fragmentation pattern of the C 1s excited CH2FCF3 molecule; ii) to examine the existence of multiple charged ions; iii) to verify if one can take advantage from the excitation of a specific site in the CH2FCF3 molecule in order to provoke specific bond fissions; iv) and to search for the feasibility of state-specific or site-specific effects in polyatomic systems such as the CH2FCF3 molecule.The results have been achieved by using photoelectron-photoion coincidence(PEPICO) and are considered in terms of fragmentation patterns after the excitation process and depending on the specific photo-excited site. In order to support the experimental data, NEXAFS spectrum at the C 1s edge simulation has been calculated at the TDDFT level while excited state geometry optimization calculations have been performed at the inner-shell multiconfigurational self-consistent field level. II- Experiment Monochromatic synchrotron radiation from the toroidal grating monochromator (TGM) beamline (energy range from 3.0 eV to 330 eV, resolution 500  EE  700) of the Laboratório Nacional


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de Luz Síncrotron (LNLS), (Campinas, Brazil), with entrance slits between 50 m and 300 m, depending on the desired photon flux, is focused onto an effusive gas jet11. The gas sample (>99.9 % purity) was commercially obtained from Dupon. The base pressure of the chamber was in the 10-8 Torr range. Throughout the experiment the pressure was maintained around 10-6 Torr. In order to avoid contributions from undesirable high order harmonics, a Ne filter (for beam energies between 11.0 and 21.6 eV) was used. Photoelectrons and photoions were extracted from the interaction region by an 750 V/cm electrostatic field, conducting the photoelectrons, without energy analysis, directly into a pair of microchannel plate (MCP) detectors. The charged fragments are driven into a Wiley and McLaren type12 time-of-flight (TOF) mass spectrometer for the mass-to-charge ratio analysis. The Photo-Electron-PhotoIon Coincidence (PEPICO) technique has been used, which allows the detection of photoelectrons in coincidence with the charged fragments. The measurements were performed with the TOF drift tube parallel to the axis of polarization of the synchrotron light. The TOF was designed to have a maximized efficiency for ions with energies up to 30 eV13. III – Theory The core-shell electronic spectrum was obtained with the Gaussian09 program package14 within the time-dependent density functional theory approximation – TDDFT – using the aug-cc-pVTZ basis set of Dunning and co-workers15 and with the hybrid version of the Perdew-Burke-Ernzerhof GGA functional (PBE0)16. The core-shell electronic spectrum at the carbon 1s edge was obtained within the restricted channel approximation where the electrons are excited from the active carbon 1s orbitals while all other occupied orbitals were kept frozen in the calculation. Excited state geometry optimizations have been calculated with the Molpro program package17 at the inner-shell multiconfigurational self-consistent field (IS-MCSCF) protocol18 in which the inner-shell orbital, here one of the C 1s orbitals, is relaxed with all other orbitals were frozen in the first step of the calculation. Then, all other coordinates, including the orbitals and the geometry, relax self consistently with the previously optimized inner shell orbital kept frozen. Dunning’s aug-cc-pVDZ basis set has been used while the states considered to the geometry relaxation were the first excited state of the carbon (CH2F) 1s orbital and the first excited state of the carbon (CF3) 1s orbital. IV- Results IV.1 – Valence-Shell Ionization The outermost orbitals of the CH2F-CF3 ground state (Cs point group, ground state 1A’) are10….(6a’’)2(16a’)2(7a’’)2(8a’’)2(17a’)2. Figure 1 shows the measured ion-mass spectra of the CH2FCF3 molecule upon valence and C 1s edge (~290 eV) photon energies. The HOMO, 17a’ orbital is predominantly of C–C σ bonding character10. Aiming to systematically investigate the fragmentation dynamics, it is appropriate to consider the regions below and above the carbon 1s ionization threshold.



Photons in the 40 to 290 eV energy range can access all fragmentation pathways linked to the direct single and multiple electron ejection of the valence orbitals. Thus, the mass spectra in the 40 to 290 eV range should allow us a reasonable comparison regarding the fragmentation profile after core electron excitation or ionization. The branching ratios (see Fig. 2), calculated by dividing the area of each peak by the sum of the areas of all peaks, show that, singly-charged fragments dominates the mass spectra, as habitual. The stability of the singly charged parent ion, which originates primarily from the single photoionization of the inner valence electrons, even in the X-ray region, is noticeable. The ionization of an electron from 7a’’ (HOMO-2), which is mainly localized on the CF3 group, and formed from F 2pπ lone-pair orbitals19 is expected to give rise to a C–F bond fission, leading to dissociation to CF2–CH2F++ F.

1x10

5

40 eV

Intensity (arb. units )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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5x10

+

CFH2

+

CF3

+

C2F3H2

4

CF2H

+ +

C2F4H2

+

H 2x10

CF

+

4

291 eV +

1x10

4

5x10

3

+

CF3

+

CF

CFH2

CF2H

C2F2H H

+

+

C 0

10

+

F

20

+

C2FH

C2

30

40

+

C2F3H2

+

+

C2F4H2 +

+

50

60

70

80

90

100 110

Mass/charge (Da)

Fig. 1 – Time-of-flight mass spectra of the CH2FCF3 at selected photon energies.

Selected photoion branching ratios in the photon energy range from 12 eV to 320 eV, are presented in Fig.2. Figure 3 shows the branching ratios for the atomic fragments, H+, C+, and F+. The threshold energies for some of the observed fragments are19: CH2FCF3+ (12.68  0.04 eV), CH2F+ (13.17  0.02 eV), CHCF2+ (16.69  0.07 eV). Across the measured energy range, the CH2CF3+ ion is the most intense signal (~ 38% - 15 %), followed by the CFH2+ (35 % - 15 %) ion. On the other hand, the intensities of the H+,C+, and F+ atomic ions increases from 0.55, 0.10, and 0.09, respectively at 35.0 eV to 7.7, 4.6, and 5.8 % at 300.7 eV, pointing out the importance of the fragmentation pattern as the photon energy increases. The present results for valence photoionization of CH2FCF3 roughly agrees with the 70 eV electron impact data20, although it seems that the heavier fragments are discriminated in the electron impact case: CFH2+ (32.2 %), CF3+ (23.0 %), C2F3H2+ (20.2 %), CFH+ (9.6 %), CF+ (5.4 %), CF2H+ (4.4 %), C2F2H+ (2.2 %). One cannot discard that the structures in the branching ratios observed between 21.6


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eV to 50.0 eV, are due to high order harmonics contributions of the beam, which are well known to be present in the TGM beamline. One should call the attention to the production of the CF2H+ ion, which comes from atomic rearrangement within the molecule during the dissociation process. In fact, the peak width of the CF2H+ is narrower than the corresponding CF2+ ion. We can understand that as follows: when CF2+ dissociates with low translational kinetic energy, its rearrangement with the H atom is favored. As the photon energy increases, so does the available energy which appears as translational kinetic energy of the fragments, consequently, this rearrangement becomes less probable.

40

21 +

C2F3H2

30

+

CF3

18 15

20

12

Branching Ratio (%)

9 10 0

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0

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35

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CF2 CF2H

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4 2

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0 16

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+

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CFH

1 0

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+

4 350

0

50

Photon Energy (eV) Fig. 2 – Branching ratios of the CH2FCF3 fragments as a function of the photon energy. For the sake of clarity some of the error bars are not shown.

8

Branching Ratios (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


+

C + F + H

7 6 5 4 3 2 1 0

0

50

100

150

200

250

300

Photon Energy (eV) Fig. 3 – Partial ion yield of the atomic fragments (H+, C+, and F+) of the CH2FCF3 molecule as a function of the photon energy.



IV.2 – Ionic Fragmentation Following C1s Edge Excitation and Ionization With the goal of studying the fragmentation dynamics following K shell excitation and ionization, the total ion yield (TIY) or X-ray absorption structure (XAS) spectrum was measured covering the C1s edge (Fig.4). The core-excited state, albeit short lived (the lifetime of C 1s core hole is about 10 fs)8, plays a critical role in initiating the fragmentation dynamics since in a core excitation process an electron might be placed in a previously vacant orbital with strong antibonding properties. Opposed to valence orbitals, that are usually delocalized all over the molecule, the C 1s orbitals are withheld near to the nucleus of the C atoms. At the resonances, the excitation takes place in a well-localized electronic state to a repulsive virtual molecular state.

AB CD E

Intensity (arb. units)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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270

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325

330

Energy (eV)

Fig. 4 – Red line: X-ray Absorption Structure (XAS) spectrum of CH2FCF3 around the C 1s-edge taken with 0.5 eV steps. Blue line: Theoretical calculations obtained at the TDDFT/PBE0/aug-ccpVTZ level, convoluted to mimic the experimental data. The discrete sticks were broadened with Gaussian functions with 0.2 eV width. A shift in the energy scale of +4.5 eV has been applied to better compare with the experimental data. Figure 4 also displays the carbon 1s core-shell electronic spectrum of the CF3CH2F molecule obtained at the TDDFT/PBE0/aug-cc-pVTZ level. An energy shift of +4.5 eV has been applied on the energy axis to better compare with the experimental data. The discrete values of the calculated oscillator strengths were broadened with Gaussian functions with 0.2 eV width. Table I shows the TD-DFT energies and the respective oscillator strengths. Peak

TD-DFT Energy (eV)

oscillator strength (a.u.)

A

284.0

0.028

B

285.1

0.017


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C

288.5

0.025

D

289.8

0.028

E

292.1

0.043

Table 1 – TDDFT/PBE0/aug-cc-pVTZ energies and oscillator strengths values of the peaks A to E and the experimental energy of the peaks. The energy values were shifted by +4.5 eV to compare with the experimental values. Also, good estimative for inner-shell ionization potentials were obtained from the calculations of Cao21

where the carbon 1s potential energy of the CH2F site of the CH3CH2F molecule was 293.4 eV and

to the CF3 site of the CH3CF3 molecule was 298.6 eV. At photon energies below the C1s edge, electrons can be promoted to the LUMO or LUMO+1 orbitals, and the inner-shell hole is replaced by a resonant Auger relaxation, that generally gives rise to singly ionized species, in which the molecule is often unstable and breaks into smaller atomic and molecular fragments. Above the C1s edge, non resonant Auger decay dominates, giving rise to double or multiple charged species that are even more unstable. As opposed to the core-excited state, the coreionized intermediate state keeps much of the bonding structure of the neutral ground state since the ejection of a core electron has no direct consequence on the bonding orbitals9. In such a way, the coreionized states are usually bound, albeit some geometry changes may succeed. The XAS (or TIY) spectrum shows an underlying continuum as a result of the direct photoionization of the valence levels. In Figure 4, the peaks A and B were attributed to the singlet excitations generated from the carbon C(H2F) 1s orbital to the natural transition orbitals22 shown in the right side of Fig.5 with energies 279.5 eV and 280.6 eV and oscillator strengths 0.028 a.u. and 0.017 a.u. respectively. The peaks C, D, and E have been assigned to the singlet excitations generated from the carbon C(F3) 1s orbital to the natural transition orbitals shown in the right side of Fig. 6 with energies 284.0 eV, 285.3 eV and 287.6 eV and oscillator strengths 0.025 a.u., 0.028 a.u., and 0.043 a.u. respectively.



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Fig.5- CF3CH2F natural transition orbitals obtained at the TDDFT/PBE0/aug-cc-pVTZ level. The peaks A and B have been assigned to the singlet excitations generated from the C(H2F) 1s to the natural transition orbitals shown in the right side of the figure.


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Fig. 6 -CF3CH2F natural transition orbitals obtained at the TDDFT/PBE0/aug-cc-pVTZ level. The peaks C, D, and E were attributed to the singlet excitations generated from the C(F3) 1s to the natural transition orbitals shown in the right side of the figure. Figure 7 shows the measured branching ratios upon C 1s excitation and ionization as a function of the photon energy. Nearby the C1s edge, the branching ratios of the C2F3H2+ ion, corresponding to the loss of a F atom, presents a peculiar photon energy dependence and is the most intense fragment (~15-22 %) followed by the CFH2+ fragment (~14 - 20 %). At 283.7 eV, corresponding to the excitation of the C(H2F) site, the yields of the C2F3H2+, CFH2+, and CF3+ ions exhibit maxima while local minima are observed in the production of CF+, CFH+ and CF2+, C+, F+, H+ ions. On the other hand, at 291.0 eV, surrounding the excitation of the C(F3) site, a different effect is observed, i.e., maxima for the C2F3H2+, CFH2+, and CF3+ fragments and minima for CF+, CFH+ and CF2+, C+, F+, H+ moieties. This site-specific fragmentation can tentatively be interpreted as a result of a dissociation of the F atom due to a highly repulsive intermediate state. It means that dissociation of the neutral F atom in the C 1s excited CF3CFH2* molecule comes from the strongly antibonding character of the LUMO or LUMO+1 orbitals to which the C 1s electron was excited to, succeed by electronic decay of the C 1s excited species. Another observation one can take from the mass spectra recorded at the 300.0 eV, in the vicinity of the C 1s ionization potential (Rydberg levels) where the electronic wave functions are less localized and the spectator Auger relaxation is more feasible to occur. At that energy, there are maxima in the ion



yields of the lighter fragments, such as H+, C+, and F+, pointing out the contribution of the C 1s ionization to the fragmentation of the molecule.The increase in the fragmentation gives rise to an increment in the neutral dissociation of CH2FCF3 to CFH2* or CF3* in a core excited state decaying to C+ plus other fragments.

+

C2F3H2

22

7,8

+

10

CF3

7,4

18

7,2

9

7,0

16 270 285 300 315

3,4

+

CFH2

20

6,8

270 285 300 315

CFH

17

270 285 300 315

+

CF

16

3,2

+

15 cf

18 3,0

14

16

13

2,8 14

+

CF2

7,6

20

Branching ratio (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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270 285 300 315

270 285 300 315

12

270 285 300 315

Photon Energy (eV) Fig. 7 – Branching ratios for the CH2FCF3 moieties as a function of the photon energy around the C1s edge. The blue line represents the total electron yield (TEY) for the sake of comparison. The full black lines were drawn to guide the eyes. In order to interpret the yields of the measured fragments presented in Fig. 7, we performed a series of quantum chemistry calculations based on the inner-shell multiconfigurational self-consistent field (IS-MCSCF) protocol18 where the active space was formed by the carbon 1s orbital plus the five highest occupied molecular orbitals and the two lower unoccupied molecular orbitals, which consist of an active space formed by eight electrons and six active orbitals (IS-MCSCF(8,6)). The coordinates of the relaxed system calculated in the first excited state of the C(H2F) 1s carbon is presented in Fig. 8. The result shows that the C(H2F) 1s excitation creates a repulsive potential which expels a fluorine atom on the 2P state leaving the heavier radical fragment C2F3H2* which could possibly relax via Auger process to the fundamental state of the ion C2F3H2+ giving rise to the maxima located at the peak-A position in the Fig.7, C2F3H2+ yield fragment. Beside the fluorine expelling, we also observed the elongation of the C-C bond from 0.151 nm, on the ground state geometry, to 0.164 nm on the final state geometry shown in Fig.8. The carbon 1s excited state is repulsive also for the C-C bond. The C-C bond elongation after the C(H2F) 1s excitation is an indication of a weakening of the C-C bond which, in turn, could explain the high yields of the CF3+ and the CH2F+ fragments with maxima near the peak-A position, as shown in Fig. 7, since it is possible that one excited state may give rise to more than one fragmentation channel.


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Fig. 8 - C(H2F) 1s first excited state relaxed geometry performed at the IS-MCSCF(8,6) level with augcc-pVDZ basis set. The C(H2F) 1s excitation creates a repulsive potential which expel a fluorine atom.

On the other hand, the first excitation from the C(F3) 1s carbon creates a repulsive potential in the C-C bond as can be seen from the result shown in Fig. 9. This behavior can be better understood if we look at the final natural transition orbital presented in Fig. 6 assigned as the peak-E. The final E natural transition orbital has a strong anti-bonding character on the C-C bond which gives rise to a repulsive potential resulting in the bond cleavage. The preferred cleavage for the C-C bond can be given as a possible explanation to the yields of the lighter fragments CFH+, CF+ and CF2+ shown on the right side of the Fig. 7, with maxima near the peak-C position. Furthermore, we point out to the branching ratio of the CF3+ and CH2F+ ions around 295 eV being 9% and 15% respectively, which shows that these ions are formed at the C(F3) 1s site excitation. But part of the CFH2* and CF3* highly excited fragments, obtained after C(F3) 1s excitation, may dissociate, relaxing the energy excess, and yielding the lighter CFH+, CF+ , and CF2+ ions.

Fig. 9 - C(F3) 1s first excited state relaxed geometry performed at the IS-MCSCF(8,6) level with aug-ccpVDZ basis set. The C(F3) 1s excitation creates a repulsive potential which cleavage the C-C bond.



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V – Conclusions In summary, we have measured the photofragmentation of CH2FCF3 using photoelectronphotoion coincidence measurements in their main categories, namely: valence ionization, core-level excitation, and core-level ionization, to investigate the interaction of the CH2FCF3 molecule with EUV and X-ray photons. It was observed that each category produces specific features in the ensuing fragmentation dynamics. One of the C atom is bonded to three fluorine atoms C(F3), while the other is bonded to two hydrogen atoms and one fluorine atom, C(H2F). The two C 1s orbitals are highly localized, respectively, on the particular carbon atom. Due to the fact that the C 1s ionization energy depend on the chemical environment of the C atom inside the CH2FCF3 molecule, the C(F3) and C(H2F) atoms exhibits distinct chemical shifts. This localization influences the fragmentation pattern, giving rise to the so-called site-specific fragmentation. From the calculations, one concludes that the C(H2F) 1s excitation creates a repulsive potential, ejecting a fluorine atom on the 2P state leaving the heavier radical fragment C2F3H2* which relaxes via Auger decay to the fundamental state of the ion C2F3H2+. Moreover, the C-C bond elongation after the C(H2F) 1s excitation indicates a weakening of the C-C bond which, gives rise to the high yields of the CF3+ and the CH2F+ fragments. On the other hand, the excitation of the C(F3) 1s carbon gives promotes a repulsive potential in the C-C bond. The preferred cleavage for the C-C bond gives rise to the yields of the lighter fragments CFH+, CF+ and CF2+.

Acknowledgements This work was supported in part by CAPES, FAPERJ, CNPq, and Laboratório Nacional de Luz Síncrotron (LNLS, Brazil).

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Fragmentation of Valence and Carbon Core Excited and Ionized

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