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Digitale Medien

Rotationally resolved pulsed field ionization photoelectron study of CO+(X 2Σ+,v+=0–42) in the energy range of 13.98–21.92 eV (1999)

Evans, M. ; Ng, C. Y.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 111 (1999), S. 8879-8892

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: We have obtained rotationally resolved pulsed field ionization–photoelectron (PFI-PE) spectra of CO in the energy range of 13.98–21.92 eV, covering the ionization transitions CO+(X 2Σ+,v+=0–42,N+)←CO(X 1Σ+,v″=0,N″). The PFI-PE bands for CO+ (X 2Σ+, v+=8–22, 24, and 28–39) obtained here represent the first rotationally resolved spectroscopic data for these states. The high-resolution features observed in the PFI-PE spectra allow the identification of vibrational bands for the CO+ (X 2Σ+, v+=10, 14, 15, 17, 18, 21, 24, 25, 29–31, 33, 35–37, and 39) states, which strongly overlap with prominent vibrational bands of the CO+(A 2Π3/2,1/2,B 2Σ+) states. The simulation using the Buckingham–Orr–Sichel model has provided accurate molecular constants for CO+(X 2Σ+,v+=0–42), including ionization energies, vibrational constants (ωe+=2218.8±3.5 cm−1, ωe+xe+=16.20±0.32 cm−1, ωe+ye+=0.074±0.011 cm−1, and ωe+ze+=−0.001 83±0.000 13 cm−1), and rotational constants [Be+=1.9797±0.0051 cm−1, αe+=0.0201±0.0011 cm−1, γe+=0.000 122±0.000 067 cm−1, ze+=−(5.2±1.1)×10−6 cm−1]. Enhancement of ΔN〈0 rotational branches, attributable to field-induced rotational autoionization, was clearly discernible in PFI-PE bands for CO+ (X 2Σ+, v+=0–5, 11, and 12). Significant local enhancements due to near-resonance autoionization were observed for low v+ (〈10) PFI-PE bands of CO+(X 2Σ+), where the density of interloper Rydberg states converging to higher ionic levels is high as manifested in the photoion spectrum. The observation of a long vibrational progression in the Franck–Condon gap region, where strong autoionization states are absent, is consistent with the suggestion that high-n Rydberg states converging to highly excited vibrational levels of CO+(X 2Σ+) are partially populated via direct excitation to a repulsive neutral state. The relatively minor band intensity variation observed for high v+ PFI-PE bands is also in accord with the direct excitation model. Since ΔN=0, ±1, ±2, and ±3 rotational branches are observed in the PFI-PE spectra, we conclude that the ejected photoelectrons are restricted to angular momentum continuum states l=0–4. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.480259

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2

Digitale Medien

Rotationally resolved pulsed field ionization photoelectron study of O2+(B 2Σg−,2Σu−; v+=0–7) at 20.2–21.3 eV (1999)

Evans, M. ; Stimson, S. ; Ng, C. Y.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 110 (1999), S. 315-327

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: We have obtained rotationally resolved pulsed field ionization photoelectron (PFI-PE) spectra of O2 in the energy range of 20.2–21.3 eV, covering the ionization transitions of O2+(B 2Σg−, v+=0–7, N+)←O2(X 3Σg−, v″=0, N″). Only the ΔN=−2, 0, and +2 (or O, Q, and S) rotational branches are observed in the PFI-PE bands for O2+(B 2Σg−, v+=0–7), indicating that the outgoing electron continuum channels with angular momenta l=1 and 3 dominate in the ionization transitions. This experiment allows the determination of accurate spectroscopic constants, such as ionization energy (20.29825±0.0005 eV) for the formation of O2+[B 2Σg−, v+=0, N+=1 (F2)] from O2(X 3Σg−, v″=0, N″=1), vibrational constants (ωe+=1152.91 cm−1, ωe+χe+=20.97 cm−1_, and rotational constants (Be+=1.255±0.0015 cm−1, αe+=0.0241±0.00037 cm−1_ for O2+(B 2Σg−, v+). The (nominal) effective lifetimes for high-n Rydberg states converging to O2+(B 2Σg−, v+=0–6) are measured to be (approximate)0.2–0.6 μs, which are significantly shorter than those of (approximate)1.9 μs observed for O2+(b 4Σg−, v+=0–5). The shorter (nominal) effective lifetimes for high-n Rydberg states converging to O2+(B 2Σg−, v+=0–6) are attributed to the higher kinetic energy releases (or velocities) of O++O fragments resulting from predissociation of the O2+(B 2Σg−, v+=0–6) ion cores. Rotationally resolved PFI-PE measurements also make possible the identification of the weak vibrational progression with the origin at 20.35 eV as associated with transitions to O2+(2Σu−, v+=0–7). The analysis of the rotationally resolved PFI-PE bands for O2+(2Σu−, v+=0 and 1) has yielded accurate rotational constants and IE values for these states. The rotational structures resolved in the O2+(2Σu−, v+=0 and 1) PFI-PE bands are contributed overwhelmingly by the ΔN=−3, −1, +1, and +3 (or N, P, R, and T) rotational branches, showing that the angular momenta for the outgoing photoelectron are restricted to l=0, 2, and 4. Based on simulation of the observed rotational structures, we also obtain the predissociative lifetimes for O2+(B 2Σg−, v+=0–7) and O2+(2Σu−, v+=0–1) to be in the range of 0.45–2 ps. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.477915

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3

Digitale Medien

A study of the dissociation of CH3CH2SH+ by collisional activation: Evidence of nonstatistical behavior (1998)

Chen, Y.-J. ; Stimson, S. ; Fenn, P. T. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 108 (1998), S. 8020-8028

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The absolute total cross sections for CH3CH2+, C2H4+, C2H3+, CH3+, CH2SH+(CH3S+), CH2S+(HCSH+), CHS+(CSH+), and H2S+ produced by the collision-induced dissociation (CID) reaction of CH3CH2SH++Ar have been measured in the center-of-mass collision energy (Ec.m.) range of 1–42 eV. Using the charge transfer probing technique, we found that the mass 47 product ions have overwhelmingly the CH2SH+ structure. The onsets for CH3CH2+, C2H4+, C2H3+, CH2SH+, H2S+, and CH3+ are consistent with their corresponding thermochemical thresholds. The formation of the higher energy channels CH3CH2++SH and CH3+CH2SH+, which involve the C–S and C–C bond scissions, are found to dominate in the entire Ec.m. range. The lower energy channel corresponding to the formation of CH3CHSH++H is not found. The strong preference observed for the formation of the higher energy channels is in accord with the conclusion obtained in the recent CID study of CH3SH+, providing evidence that the CID of CH3CH2SH+ is also nonstatistical. The high yields of CH3CH2++SH and CH2SH++CH3 are attributed to the more efficient translational to vibrational energy transfer for the low frequencies C–S and C–C stretching modes than for the high frequencies C–H and S–H stretching modes, along with the weak couplings between these low and high frequencies vibrational modes of CH3CH2SH+. The relative abundances of product ions formed by the single-photon ionization of CH3CH2SH were also measured for comparison with the CID results. The CH3CHSH++H channel is observed in the photoionization of CH3CH2SH. Similar to the finding in the photoionization of CH3SH, the relative abundances of fragment ions formed in the photoionization of CH3CH2SH are in qualitative accord with statistical predictions. To rationalize the dissociation mechanisms of CH3CH2SH+, we have also performed ab initio calculations to locate the possible transition structures for the observed dissociation channels. © 1998 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.476241

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4

Digitale Medien

Direct Identification of Photofragment Structures Formed in the 193 nm Photodissociation of Thiophene (1995)

Hsu, C.-W. ; Liao, C.-L. ; Ma, Z.-X. ; [weitere]

s.l. : American Chemical Society

The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 1760-1767

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Quelle: ACS Legacy Archives

Thema: Chemie und Pharmazie , Physik

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1021/j100006a019

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5

Digitale Medien

High-resolution pulsed field ionization photoelectron study of O2: Predissociation lifetimes and high-n Rydberg lifetimes converging to O2+(c 4Σu−, v+=0,1) (1998)

Evans, M. ; Stimson, S. ; Ng, C. Y.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 109 (1998), S. 1285-1292

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: We have measured the pulsed field ionization photoelectron (PFI-PE) spectrum of O2 in the energy range of 24.53–25.0 eV at a PFI-PE resolution of 11 cm−1 (full width at half maximum, FWHM). The PFI-PE bands for O2+(c 4Σu−, v+=0 and 1) obtained at O2 rotational temperatures of 35 and 298 K have been simulated using the Buckingham–Orr–Sichel model. Only the ΔN=−3, −1, +1, and +3 (or N, P, R, and T) rotational branches are observed, indicating that the outgoing electron continuum channels with angular momenta l=0, 2, and 4 dominate in the threshold ionization transitions O2+(c 4Σu−, v+=0 to 1, N+)←O2(X 3Σg−, v″=0, N″). The simulation yields natural rotational linewidths of 19.6±2.0 and 77±8 cm−1 (FWHM) for the respective v+=0 and 1 PFI-PE bands of the O2+(c 4Σu−) state. These linewidths make possible the determination of the predissociation lifetimes for the v+=0 and 1 levels of O2+(c 4Σu−) to be (2.7±0.3)×10−13 and (6.9±0.7)×10−14 s, respectively. This experiment also provides accurate ionization energies of 24.56227±0.0005 and 24.75445±0.0005 eV for transitions to O2+(c 4Σu−, v+=0, N+=0) and O2+(c 4Σu−, v+=1, N+=0) from O2(X 3Σg−, v″, N″=1), respectively. The rotational constants of 1.58±0.02 and 1.54±0.04 cm−1 obtained here for the O2+(c 4Σu−, v+=0) and O2+(c 4Σu−, v+=1) states allow the calculation of their corresponding equilibrium bond distances to be 1.155±0.011 and 1.170±0.015 Å. The (nominal) effective lifetimes for high-n Rydberg states converging to the O2+(c 4Σu−, v+=0 and 1) states are measured to be (approximate)0.33 μs, which are significantly shorter than the values of (approximate)1.9 μs measured for the O2+(b 4Σg−, v+=0–5) states. The shorter (nominal) effective lifetimes for high-n Rydberg states converging to O2+(c 4Σg−, v+=0 and 1) observed are attributed to the higher kinetic energy releases (or velocities) of O+ fragments resulting from predissociation of the O2+ ion cores. © 1998 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.476678

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Digitale Medien

A molecular beam photoionization mass spectrometric study of Cr(CO)6, Mo(CO)6, and W(CO)6 (1997)

Chen, Y.-J. ; Liao, C.-L. ; Ng, C. Y.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 107 (1997), S. 4527-4536

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The photoionization efficiency (PIE) spectra for M(CO)n+ (n=0–6) from M(CO)6, M=Cr, Mo, and W, have been measured in the photon energy range of 650–1600 Å. Based on the ionization energies for M(CO)6 and appearance energies (AEs) for M(CO)n+ (n=0–5) determined here, we have obtained estimates for the sequential bond dissociation energies (D0) for CO–M(CO)n−1+ (n=1–6). The comparison between the D0 values for the Cr(CO)6+ system obtained here and in the recent collisional induced dissociation and theoretical studies suggests that D0 values for CO–M(CO)n−1+ (n=3–6) based on this PIE experiment are reliable. The PIE results reveal the general trend for individual D0 values that D0[CO–Cr(CO)n−1+]〈D0[CO–Mo(CO)n−1+]〈D0[CO–W(CO)n−1+] (n=3–6). The comparison of the first D0 values for M(CO)6+ obtained here and those for M(CO)6 reported previously provides strong support for the theoretical analysis that the importance of relativistic effects, which give rise to more efficient M to CO π-back-donation in M(CO)6, is in the order W(CO)6〉Mo(CO)6〉Cr(CO)6. © 1997 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.474814

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Digitale Medien

A state-selected study of the ion–molecule reactions O+(2D,2P)+H2O (1997)

Li, X. ; Huang, Y.-L. ; Flesch, G. D. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 106 (1997), S. 928-933

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: State-selected absolute cross sections for H2O+ and OH+ formed by the O+(2D,2P)+H2O reactions have been measured in the center-of-mass collision energy (Ec.m.) range of (approximate)0.10–30 eV. The charge transfer cross sections for O+(2D)+H2O are significantly higher than those for O+(4S)+H2O. This observation is attributed to the increased number of accessible exothermic product channels for O+(2D)+H2O. While the H2O+ cross sections for O+(2P)+H2O are comparable to those from O+(4S)+H2O at Ec.m.≥1 eV, the H2O+ cross sections for O+(2P)+H2O at Ec.m.〈1 eV are substantially lower than those for O+(4S)+H2O. The lower H2O+ cross sections observed for O+(2P)+H2O are rationalized as due to further dissociation of excited charge transfer H2O+ ions and/or the efficient competition of the OH++OH product channel. The cross sections for OH+ from O+(2D,2P)+H2O are significantly greater than those from O+(4S)+H2O. The majority of OH+ ions from O+(2D,2P)+H2O are associated with exothermic channels corresponding to the formation OH+(X 3Σ−,1Δ,A 3Π)+OH. The comparison of the sum (σT) of the cross sections for H2O+ and OH+ from O+(4S)+H2O to those from O+(2D)+H2O and O+(2P)+H2O shows that σT's for O+(4S)+H2O and O+(2P)+H2O are comparable, whereas the σT values for O+(2D)+H2O are greater than those for O+(4S)+H2O and O+(2P)+H2O. The σT values are found to conform with the 1/Ec.m. dependence at low Ec.m.'s, indicating that the ion–dipole interaction plays an important role in the formation of the long-lived collision complexes. The high cross sections for H2O+ and OH+ from O+(2D,2P)+H2O observed here suggest that these reactions should be included in the simulation of the H2O+ and H3O+ ion density data obtained in space-borne mass spectrometric experiments. © 1997 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.473172

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A high resolution energy-selected kinetic energy release study of the process SF6+hν→SF5++F+e−: Heat of formation of SF5+ (1997)

Evans, M. ; Ng, C. Y.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 106 (1997), S. 978-981

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: Using the newly constructed photoelectron-photoion coincidence apparatus associated with the chemical dynamics beamline at the advanced light source, we have performed a high resolution energy-selected kinetic energy release measurement for the dissociative photoionization process SF6+hν→SF5++F+e−. After taking into account the center-of-mass kinetic energy release, the thermochemical threshold for this process is determined to be 14.11±0.08 eV. This value yields 18.5±1.9 and −202.9±2.2 kcal/mol for the heats of formation at 0 K for SF5+ and SF5, respectively. © 1997 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.473963

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9

Digitale Medien

Absolute state-selected total cross sections for the ion–molecule reactions O+(4S,2D,2P)+H2(D2) (1997)

Li, X. ; Huang, Y.-L. ; Flesch, G. D. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 106 (1997), S. 564-571

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: Absolute total cross sections for the state-selected reactions of O+(4S,2D,2P)+H2 (D2) have been measured in the center-of-mass collision energy (Ec.m.) range of 0.02–12 eV. The cross sections for OH+ (OD+) from O+(2D)+H2 (D2) are slightly higher than those from O+(4S)+H2 (D2), whereas the OH+ (OD+) cross sections from O+ (2P)+H2 (D2) are (approximate)40% lower than those from O+(4S)+H2 (D2) and O+ (2D)+H2 (D2). At Ec.m.〈0.5 eV, the total cross sections for OH+ (OD+) from O+ (4S)+H2 (D2) and O+(2D)+H2 (D2) are in accord with those predicted by the Langevin–Gioumousis–Stevenson model. Significantly higher cross sections are observed for H+ (D+) and H2+ (D2+) from O+(2D)+H2 (D2) and O+(2P)+H2 (D2), as compared to those from O+(4S)+H2 (D2). The exothermic nature of the O+(2D,2P)+H2 (D2) charge transfer collisions accounts for the high cross sections observed for H2+ (D2+). While the H+ (D+) ions observed in the O+(4S)+H2 (D2) reaction are identified with the H+ (D+)+O+H channel, the H+ (D+) ions from the reactions involving O+(2D) and O+(2P) are associated mostly with the H+ (D+)+OH (OD) channel, the formation of which obeys the spin-conservation rule. The comparison of the sum (σT) of cross sections for OH+ (OD+), H2+ (D2+), and H+ (D+) from O+(4S)+H2 (D2) to those from O+(2D)+H2 (D2) and O+(2P)+H2 (D2) shows that the σTs for O+(4S)+H2 (D2), O+(2D)+H2 (D2), and O+(2P)+H2 (D2) at Ec.m.〈0.5 eV are comparable. At Ec.m.〉0.5 eV, the σTs for O+(2P)+H2 (D2) are greater than those for O+(2D)+H2 (D2), which in turn are greater than those for O+(4S)+H2 (D2). This observation is attributed to the increase in the number of accessible product channels for reactions involving the excited O+(2D) and O+(2P) reactant ions. © 1997 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.473395

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Digitale Medien

A state-selected study of the ion–molecule reactions O+(4S,2D,2P)+N2 (1997)

Li, X. ; Huang, Y.-L. ; Flesch, G. D. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 106 (1997), S. 1373-1381

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: Absolute state-selected cross sections for the reactions O+(4S,2D,2P)+N2→N2++O, NO++N, and N++NO (and/or N++N+O) have been measured in the center-of-mass collision energy (Ec.m.) range of 0.06–40 eV employing the differential retarding potential method and the O+(2D) and O+(2P) ion state-selection schemes we developed recently. Charge transfer is the overwhelming product channel for the O+(2D)+N2 and O+(2P)+N2 reactions. Contrary to the results of previous experiments, the charge transfer cross sections for O+(2P)+N2 are found to be 30%–100% greater than those for O+(2D)+N2. This observation suggests that N2 is an excellent quenching gas for O+(2D,2P). While the Ec.m. dependencies for the cross sections of NO+ from O+(4S)+N2 and O+(2D)+N2 are similar, exhibiting a broad maximum in the Ec.m. range of 1.5–8 eV, the cross section for NO+ from O+(2P)+N2 is found to decrease as Ec.m. is decreased. The N+ signal observed in the O+(4S)+N2 reaction is attributed to the formation of N++N+O. The pathway of O++N2→N++NO to generate N+ is strongly suggested as the major channel in the reactions of O+(2D,2P)+N2, as evidenced by the observation of N+ well below the thermochemical thresholds of O+(2D,2P)+N2→N++N+O. © 1997 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.474087

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