Transition from Hund's coupling case (a) to case (b) in CaF ( A( 2Π Ω )) , obtained from the Ca( 3 P J)+ CF 2 Cl 2→ CaF( A( 2Π Ω ))+ CFCl 2 reaction, induced by collisional energy (original) (raw)
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Journal of Physical Chemistry A, 2003
Chemiluminescent reactions of hyperthermal Ca( 3 P) with CF 2 Cl 2 and CF 2 dCCl 2 were studied in a beam-gas arrangement under single collision conditions. Emissions associated with the A( 2 Π Ω ) f X( 2 Σ + ) and the B( 2 Σ + ) f X( 2 Σ + ) transitions from CaCl and CaF were observed for both reactions. The chemical and electronic branching ratios were determined for these reactions, and different results were obtained for each one. The different behavior was rationalized by a simple MO pictures. For the case of the reaction with CF 2 Cl 2 it was assumed that an electron from Ca( 3 P) is transferred to a σ*(C-Cl) orbital in CF 2 Cl 2 which, at higher translational energies can also enter into a σ*(C-F) orbital of the same molecule. In both cases the molecular anion produced is short-lived and will undergo fast decay to Clor Fto yield CaCl and CaF. For the reaction with CF 2 dCCl 2 the electron from Ca( 3 P) is transferred to a π* orbital of the reagent molecule that generates a relatively stable molecular anion with 2 Π symmetry. This anion subsequently cross over several repulsive 2 Σ surfaces associated with σ* orbitals of the C-Cl and the C-F bonds, to dissociate into Clor Fto produce CaCl and CaF. The electronic branching ratios are in good agreement with statistical distribution based on information theory approach, assuming the rigid rotor harmonic oscillator (RROH) approximation for the reaction with CF 2 Cl 2 and the formation of a collision complex for the reaction with CF 2 dCCl 2 .
24. X-ray excited optical luminescence (XEOL) studies of CaF2 at the Ca L2,3-edge
Journal of Electron Spectroscopy and Related Phenomena, 2001
We report a study of the optical response of CaF specimens (crystal and powder) with excitation photon energy tuned 2 across the Ca Ledge. The luminescence was in turn used to monitor the absorption across the Ca Ledge (optical XAFS). 3,2 It is found that the photoluminescence yield produces an inverted spectrum. This observation is interpreted in terms of total absorption (thickness effect), the change in decay dynamics below and above the edge and the atomic origin of the luminescence. By comparing crystal and powder results, we find that the surface component of CaF exhibits a positive shift 2 (|0.15 eV) relative to the bulk at the p–d resonance at the Ca Ledge. A DFT calculation has been carried out and it is in 3,2 good accord with the experiment. The implications of these results are discussed.
Chemical Physics, 1982
Photoion-photoelectron coincidence spectra are reported for CFaI in the region of se g2E,, and the z*E,, electronic states of the molecular cation (i.e. 10.2-11.8 ev). WiLti this energy range CI$X 'Ai) + 1(X ZPsn) are the only accessible fragments. The kinetics and the translational energy release of this dissociation process are examined. The enthalpy of formation of CF; is found to be AH8 (CF$) = 402 * 5 kJ mar I, in agreement with earIier literature values. The irrpiications of the present study for the recently reported muItiphoton dissociation ofCFaIt are discussed.
The Journal of Chemical Physics, 1999
Efficient long-range collisional energy transfer between the E0g+(3P2) and D0u+(3P2) ion-pair states of I2, induced by H2O, observed using high-resolution Fourier transform emission spectroscopy J. Chem. Phys. 135, 114302 (2011) Energy transfer of highly vibrationally excited naphthalene: Collisions with CHF3, CF4, and Kr J. Chem. Phys. 135, 054311 (2011) H+ versus D+ transfer from HOD+ to N2: Mode-and bond-selective effects J. Chem. Phys. 135, 044305 (2011) Multimode calculations of rovibrational energies and dipole transition intensities for polyatomic molecules with torsional motion: Application to H2O2 J. Chem. Phys. 135, 014308 State-to-state dynamics at the gas-liquid metal interface: Rotationally and electronically inelastic scattering of NO[21/2(0.5)] from molten gallium
Arxiv preprint arXiv: …, 2011
We present a study of dissociative electron attachment and vibrational excitation processes in electron collisions with the CF 3 Cl molecule. The calculations are based on the two-dimensional nuclear dynamics including the C-Cl symmetric stretch coordinate and the CF 3 symmetric deformation (umbrella) coordinate. The complex potential energy surfaces are calculated using the ab initio R-matrix method. The results for dissociative attachment and vibrational excitation of the umbrella mode agree quite well with experiment while the cross section for excitation of the C-Cl symmetric stretch vibrations is about a factor of three low as compared to experimental data. 1 12 Dissociative electron attachment (DEA) to polyatomic molecules typically involves mul-13 tidimensional nuclear dynamics. However, because of big computational work necessary 14 to obtain multidimensional complex (i.e., including both real and imaginary parts) energy 15 surfaces, most of theoretical DEA calculations were performed in one-dimensional approx-16 imation. In these calculations it is usually assumed that the DEA process involves one 17 reaction (dissociating) coordinate, roughly corresponding to one of the normal modes of the 18 target molecule. This approximation is sometimes too crude, and sometimes completely un-19 justified. Therefore, a lot of effort was devoted recently to calculations of multidimensional 20 DEA dynamics [1-6]. These calculations address two important problems in the physics of 21 DEA processes. First, we want to know which dissociation channels are the most important 22
The Journal of Physical Chemistry A, 1998
The F + CH 3 COCl and H + ICH 2 COCl reaction systems were studied by the infrared chemiluminescence method in a flow reactor. The primary reaction of F + CH 3 COCl gives a nascent HF(V) distribution of P 1-P 3) 21:52:27. A linear surprisal analysis gives P 0) 3 and 〈f v (HF)〉) 0.60, which is typical for H abstraction reactions by F atoms. The C-H bond energy in acetyl chloride is estimated as e101.2 kcal mol-1 , from the highest HF(V, J) level populated in the primary reaction. The H + ICH 2 COCl primary reaction leads to HI + CH 2 COCl. The secondary F + CH 2 COCl and H + CH 2 COCl reactions give chemically activated FCH 2 COCl*/CH 3 COCl* molecules. The 1,2-HCl elimination channel is the dominant unimolecular pathway for both reactions under our experimental conditions. The HCl(V) distribution from CH 3 COCl* is P 1-P 4) 39:32:20:9. Surprisal analysis was used to estimate the P 0 value as 36% and 〈f v (HCl)〉) 0.12. The reaction time had to be increased from e0.2 ms to g0.5 ms to record the HCl(V) emission from F + CH 2-COCl, and the best distribution was P 1-P 4) 68:24:5:3. The estimated 〈f v (HCl)〉 was only 0.06 which is a lower limit due to HCl(V) relaxation. The CO(V) 1 f 0) emission could also be observed from this reaction with an intensity that was typically less than 10% of the HCl(V) emission. Ab initio calculations for FCH 2-COCl at MP2/6-31G* level give the threshold energy for HCl elimination as 61 kcal mol-1 , which is 12 kcal mol-1 larger than that for CH 3 COCl at the same level. The threshold energies for the other reactions of FCH 2 COCl are 81.0 for CO elimination, 82.5 for CC dissociation, and 78.4 for C-Cl dissociation. RRKM and ab initio calculations indicate that CO formation results from the FCH 2 COCl f FCH 2 + COCl dissociation step followed by COCl f CO + Cl. For CH 3 COCl*, with 105 kcal mol-1 energy, HCl elimination accounts for 98% of the total reaction and CC dissociation accounts for the rest. The C-Cl dissociation channel is not important for either molecule at these energies.
Unimolecular Reactions of CF2ClCFClCH2F and CF2ClCF2CH2Cl: Observation of ClF Interchange
The Journal of Physical Chemistry A, 2008
The unimolecular reactions of CF 2 ClCFClCH 2 F and CF 2 ClCF 2 CH 2 Cl molecules formed with 87 and 91 kcal mol-1 , respectively, of vibrational energy from the recombination of CF 2 ClCFCl with CH 2 F and CF 2 ClCF 2 with CH 2 Cl at room temperature have been studied by the chemical activation technique. The 2,3-and 1,2-ClF interchange reactions compete with 2,3-ClH and 2,3-FH elimination reactions. The total unimolecular rate constant for CF 2 ClCF 2 CH 2 Cl is 0.54 (0.15 × 10 4 s-1 with branching fractions for 1,2-ClF interchange of 0.03 and 0.97 for 2,3-FH elimination. The total rate constant for CF 2 ClCFClCH 2 F is 1.35 (0.39 × 10 4 s-1 with branching fractions of 0.20 for 2,3-ClF interchange, 0.71 for 2,3-ClH elimination and 0.09 for 2,3-FH elimination; the products from 1,2-ClF interchange could be observed, but the rate constant was too small to be measured. The D(CH 2 F-CFClCF 2 Cl) and D(CH 2 Cl-CF 2 CF 2 Cl) were evaluated by calculations for some isodesmic reactions and isomerization energies of CF 3 CFClCH 2 Cl as 84 and 88 kcal mol-1 , respectively; these values give the average energies of formed molecules at 298 K as noted above. Density functional theory was used to assign vibrational frequencies and moments of inertia for the molecules and their transition states. These results were combined with statistical unimolecular reaction theory to assign threshold energies from the experimental rate constants for ClF interchange, ClH elimination and FH elimination. These assignments are compared with results from previous chemical activation experiments with CF 3 CFClCH 2 Cl, CF 3 CF 2 CH 3, CF 3 CFClCH 3 and CF 2 ClCF 2 CH 3 .