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Notes: A detailed three-dimensional quantum mechanical study of the (Ar+H2)+ system along the energy range 0.4 eV≤Etot≤1.65 eV is presented. The main difference between this new treatment and the previously published one [J. Chem. Phys. 87, 465 (1987)] is the employment of a new version of the reactive infinite-order sudden approximation (IOSA), which is based on the ordinary inelastic IOSA carried out for an optical potential. In the numerical treatment we include three surfaces (only two were included in the previous treatment), one which correlates with the Ar+H+2 system and two which correlate with the two spin states of Ar+(2Pj); j=3/2,1/2. The results are compared with both trajectory-surface-hopping calculations and with experiments. In most cases, very good agreement is obtained.

Notes: We have measured the time-of-flight (TOF) spectra for SCH3, CH3, and SSCH3 formed in the photodissociation processes, CH3SSCH3+hν(193 nm)→2SCH3 and CH3+SSCH3. The dissociation energies for the CH3S–SCH3 and CH3SS–CH3 bonds determined at 0 K by the TOF measurements are 72.4±1.5 and 55.0±1.5 kcal/mol, in agreement with the literature values. The threshold value for the formation of S2 measured by the TOF spectrum for S2 is in accord with the thermochemical threshold for the process, SSCH3+hν(193 nm) →S2+CH3. The threshold energy determined from the TOF spectrum for S is found to be consistent with the thermochemical threshold for the photodissociation process, SCH3+hν(193 nm) →S(1D)+CH3, an observation supporting that S atoms are not produced in the ground S(3P) state in the 193 nm photodissociation of SCH3. This observation is rationalized by symmetry correlation arguments applied between the S+CH3 product and SCH3 states.

Notes: We have measured the translational energy releases of the laser photodissociation processes CH3SCH3+hν (193 nm)→CH3+CH3S [process (1)] and CH3SCH2+H [process (2)]; and CH3S+hν (193 nm)→S+CH3 [process (3)]. The onsets of the translational energy distributions for photofragments of processes (1) and (2) allow the direct determination of 74.9±1.5 and 91±2.5 kcal/mol for the dissociation energies of the CH3–SCH3 and H–CH2SCH3 bonds at 0 K, respectively. The threshold observed for S formed by process (3) is consistent with the conclusion that the production of S(3P) is small compared to S(1D). The photoelectron–photoion coincidence (PEPICO) spectra for CH3SCH+3, CH3SCH+2, CH3S+ (or CH2SH+ ), and CH2S+ resulting from photoionization of CH3SCH3 have been measured in the wavelength region of 900–1475 A(ring). The PEPICO study allows the construction of a detailed breakdown diagram for the formation of CH3SCH+2, CH3S+ (or CH2SH+ ), and CH2S+ from energy-selected CH3SCH+3 ions.

Notes: The kinetic energy releases of the photodissociation processes, CH3SH+hν (193 nm)→CH3+SH, CH3S+H, and CH2S+H2, have been measured using the time-of-flight mass spectrometric method. These measurements allow the direct determination of the dissociation energies for the CH3–SH and CH3S–H bonds at 0 K as 72.4±1.5 and 90±2 kcal/mol, respectively. The further dissociation of SH according to the process SH+hν (193 nm)→S+H has also been observed. The appearance energy (AE) of S produced in the latter process is consistent with the formation of S(3P)+H. The photoelectron–photoion coincidence (PEPICO) spectra for CH3SH+, CH3S+ (or CH2SH+), and CH2S+ from CH3SH have been measured in the wavelength range of 925–1460 A(ring). The PEPICO measurements make possible the construction of the breakdown diagram for the unimolecular decomposition of internal-energy-selected CH3SH+ in the range of 0–83 kcal/mol. The AE measured for CH2S+ is consistent with the conclusion that the activation energy is negligible for 1,2-H2 elimination from CH3SH+.

Notes: Total state-selected and state-to-state absolute cross sections for the reactions Ar+(2P3/2,1/2)+H2(X,v=0)→Ar (1S0)+H+2(X˜,v') [reaction (1)], ArH++H [reaction (2)], and H++H+Ar [reaction (3)] have been measured in the center-of-mass collision energy Ec.m. range of 0.24–19.1 eV. Absolute spin–orbit state transition total cross sections (σ3/2→1/2,σ1/2→3/2) for the collisions of Ar+(2P3/2,1/2) with H2 at Ec.m.=1.2–19.1 eV have been obtained.The measured state-selected cross sections for reaction (1) [σ3/2,1/2(H+2)] reveal that at Ec.m.≤5 eV, σ1/2(H+2) is greater than σ3/2(H+2), while the reverse is observed at Ec.m.≥7 eV. The total state-to-state absolute cross sections for reaction (1) (σ3/2,1/2→v') show unambiguously that in the Ec.m. range of 0.16–3.9 eV the dominant product channel formed in the reaction of Ar+(2P1/2)+H2(X,v=0) is H+2(X˜,v'=2)+Ar. These observations support the conclusion that at low Ec.m. the outcome of charge transfer collisions is governed mostly by the close energy resonance effect. However, at sufficiently high Ec.m.(〉6 eV) the charge transfer of Ar+(2P3/2)+H2 is favored compared to that of Ar+(2P1/2)+H2.The relative values measured for X1/2→v'[≡σ1/2→v'/σ1/2 (H+2)] are in good accord with those predicted from calculations using the state-to-state cross sections for the H+2(X˜,v'=0–4)+Ar charge transfer reaction and the relation based on microscopic reversibility. The experimental values for X3/2→v'[≡σ3/2→v'/σ3/2 (H+2)] and those predicted using the microscopic reversibility argument are also in fair agreement. The spin–orbit effect for the cross section of reaction (2) [σ3/2,1/2(ArH+)] is significantly less than that for reaction (1). Both σ3/2(ArH+) and σ1/2(ArH+) decrease rapidly as Ec.m. is increased, and become essentially identical at Ec.m. ≈3.8 eV. The cross sections for reaction (3) observed in the Ec.m. range of 2.5–12 eV are ≤3% of σ3/2,1/2(H+2).The onset for the formation of H+ by reaction (3) is consistent with the thermochemical threshold. The values for σ3/2→1/2 and σ1/2→3/2 observed here are nearly a factor of 2 greater than those measured by the energy loss spectroscopic method. However, the kinetic energy dependencies for σ3/2→1/2 and σ1/2→3/2 are in accord with the previous measurements. Theoretical cross sections for the charge transfer and spin–orbit state transition reactions are calculated at Ec.m.=19.3 eV using the nonreactive infinite-order sudden approximation for comparison with experimental values.

Notes: Absolute spin–orbit state-selected total cross sections for the reactions, Ar+(2P3/2,1/2)+O2→O+2+Ar [reaction (1)], O++O+Ar [reaction (2)], and ArO++O [reaction (3)], have been measured in the center-of-mass collision energy (Ec.m.) range of 0.044–133.3 eV. Absolute spin–orbit state transition total cross sections for the Ar+(2P3/2,1/2)+O2 reaction at Ec.m.=2.2–177.6 eV have also been examined. The appearance energies for the formation of O+ (Ec.m.=2.9±0.2 eV) and ArO+ (2.2±0.2 eV) are in agreement with the thermochemical thresholds for reactions (2) and (3), respectively. The cross sections for O+2, O+, and ArO+ depend strongly on Ec.m. and the spin–orbit states of Ar+, suggesting that reactions (1)–(3) are governed predominantly by couplings between electronic potential energy surfaces arising from the interactions of Ar+(2P3/2)+O2, Ar+(2P1/2)+O2, and O+2+Ar.In the Ec.m. range of 6.7–22.2 eV, corresponding to the peak region of the O+ cross section curve, the cross sections for O+ are ≥50% of those for O+2. The production of O+ by reaction (2) is interpreted to be the result of predissociation of O+2 in excited states formed initially by reaction (1). The formation of charge transfer O+2(a˜ 4Πu) has been probed by the charge transfer reaction O+2(a˜ 4Πu)+Ar. The results indicate that in the Ec.m. range of 0.4–3.0 eV charge transfer product O+2 ions are formed mainly in the O+2(a˜ 4Πu) state. Experimental evidence is found supporting the conclusion that the vibrational distributions of O+2(a˜ 4Πu) formed in reaction (1) and by photoionization of O2 in the energy range between the O+2(a˜ 4Πu, v=0) and O+2(A˜ 2Πu, v=0) thresholds are similar.The population of O+(4S) formed by reaction (2) has also been measured by the reaction O+(4S)+N2→NO++N. In the Ec.m. range of 3–44 eV, product O+ ions of reaction (2) are shown to be dominantly in the O+(4S) ground state. At Ec.m.≥14 eV, the retarding potential energy analysis for O+2 shows that more than 98% of the charge transfer O+2 ions are slow ions formed mostly by the long-range electron jump mechanism. Product ArO+ ions are observed only in the Ec.m. range of 2.2–26.6 eV. At Ec.m. slightly above the thermochemical thresholds of reactions (2) and (3), the overwhelming majority of ArO+ and O+ ions are scattered backward and forward with respect to the c.m. velocity of reactant Ar+, respectively. This observation is rationalized by a charge transfer predissociation mechanism which involves the formation of ArO+ and O+ via nearly collinear Ar+–O–O collision configurations at Ec.m. near the thresholds of reactions (2) and (3).

Notes: Absolute spin–orbit state-selected total cross sections for the reactions, Ar+(2P3/2,1/2)+CO→CO++Ar [reaction (1)], C++O+Ar [reaction (2)], O++C+Ar [reaction (3)], and ArC++O [reaction (4)], have been measured in the center-of-mass collision energy (Ec.m.) range of 0.04–123.5 eV. Absolute spin–orbit state transition total cross sections for the Ar+(2P3/2,1/2)+CO reactions at Ec.m. have also been obtained. The appearance energies (AE) for C+(Ec.m.=6.6±0.4 eV) and O+(Ec.m.=8.6±0.4 eV) are in agreement with the thermochemical thresholds for reactions (2) and (3), respectively. The observed AE for reaction (4) yields a lower bound of 0.5 eV for the ArC+ bond dissociation energy. The kinetic energy dependence of the absolute cross sections and the retarding potential analysis of the product ions support that ArC+, C+, and O+ are formed via a charge transfer predissociation mechanism, similar to that proposed to be responsible for the formation of O+ (N+) and ArO+ (ArN+) in the collisions of Ar+(2P3/2,1/2)+O2(N2).

Notes: A novel diol based metalorganic route has been developed and employed to deposit BaTiO3 films on Si and Pt coated Si substrates. Differential thermal analysis, thermogravimetric analysis, x-ray photoelectron spectroscopy, and x-ray diffraction collectively indicated that BaTiO3 was formed through the reaction of Ba and Ti oxides at approximately 500 °C. The films were single phase, had no crystallographic texture, and contained no detectable impurities. © 1995 American Institute of Physics.

Notes: A crossed laser and molecular beam photofragmentation apparatus is described. The apparatus is equipped with a rotatable molecular beam source and a translationally movable ultrahigh vacuum mass spectrometer for time-of-flight (TOF) measurements. Using this apparatus we have measured the TOF spectra of S and CS resulting from the photofragmentation processes, CS2+hν(193 nm)→CS(X,v)+S(1D or 3P). The translational energy distributions of photofragments derived from the S and CS TOF spectra are in good agreement. This observation, together with the finding that the TOF spectra of S and CS are independent of laser power in the 25–150 mJ range, shows that the further absorption of a laser photon by CS to form C(3P)+S(3P) within the laser pulse is insignificant. The TOF spectra of S obtained at electron ionization energies of 20 and 50 eV are indiscernible, indicating that the contribution to the TOF spectrum of S from dissociative ionization of CS is negligible at electron impact energies ≤50 eV. The thermochemical thresholds for the S(1D) and S(3P) channels are determined to be 18.7 and 45.0±0.4 kcal/mol, respectively, consistent with literature values. Structures found in the translational energy distribution can be correlated with vibrational structures of CS(X,v=0–5) associated with the S(1D) channel. The translational energy distribution supports the previous observation that the vibrational state distribution of CS(X,v) is peaked at v=3. The TOF experiment is also consistent with the S(3P)/S(1D) ratio of 2.8±0.3 determined in a recent vacuum ultraviolet laser induced fluorescence measurement on the S photofragment. Photofragments from CS2 clusters are observed at small laboratory angles with respect to the CS2 beam direction and are found to have velocity distributions peaked at the CS2 cluster beam velocity.