Infrared Vacuum-Ultraviolet Laser Pulsed Field Ionization-Photoelectron Study of CH 3 Br + ( X̃ 2 E 3/2 )

et al. 2013

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Two-color visible-ultraviolet (VIS-UV) resonance-enhanced laser photoionization and pulsed field ionization-photoelectron (PFI-PE) study of gaseous titanium monoxide (TiO) in the total energy range of 55,000-57,320 cm(-1) has been conducted. The TiO molecules were selectively excited to single J' rotational levels of the intermediate TiO*(B(3)Π1, ν' = 0) state by using a VIS dye laser and then ionized by using another UV laser. This two-color photoexcitation method has allowed the measurement of cleanly J(+)-resolved PFI-PE spectra for the TiO(+)(X (2)Δ(5/2,3/2); v(+) = 0, 1, and 2) vibrational bands. By simulating the rotationally resolved PFI-PE spectra, J(+) = 3∕2 is determined to be the lowest rotational level of the ground electronic state, confirming that the symmetry of the TiO(+) ground state is (2)Δ(3/2). Irregular intensity patterns for rotational PFI-PE peaks that deviated from the regular patterns that favor the rotational transitions with small change of the core rotational angular momentum, are observed. This observation is indicative of strong perturbations of the PFI-PE rotational transitions, possibly by a channel-coupling mechanism. The analysis of the PFI-PE spectra yields highly precise values for the adiabatic ionization energy of TiO [IE(TiO) = 55 005.4 ± 0.8 cm(-1) (6.81980 ± 0.00010 eV)], and the vibrational frequency (ωe(+) = 1056.1 ± 0.8 cm(-1)), the anharmonicity constant (ωe(+)χe(+) = 4.4 ± 0.8 cm(-1)), the rotational constants (B(e)(+) = 0.5613 ± 0.0009 cm(-1) and αe(+) = 0.0029 ± 0.0008 cm(-1)), and the equilibrium bond length (r(e)(+) = 1.583 Å) for the TiO(+)(X (2)Δ(3/2)) ground state, the vibrational frequency (ωe(+) = 1058.4 ± 0.8 cm(-1)), the anharmonicity constant (ωe(+)χe(+) = 5.1 ± 0.8 cm(-1)), the rotational constants (B(e)(+) = 0.5715 ± 0.0007 cm(-1) and αe(+) = 0.0030 ± 0.0004 cm(-1)) and the equilibrium bond length (r(e)(+) = 1.568 Å) for the excited spin orbit state TiO(+)(X (2)Δ(5/2)), along with the spin-orbit coupling constant (A = 105.9 ± 0.2 cm(-1)) for TiO(+)(X (2)Δ(5/2,3/2)).

Section: Resultssupporting

confidence: 91%

Section: Resultsmentioning

confidence: 99%

Rovibronically selected and resolved two-color laser photoionization and photoelectron study of titanium monoxide cation

et al. 2013

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“…This observation is consistent with the N + changes observed in the state-to-state photoionization studies of CH 3 I, CH 3 Br, FeC, and NiC. 10,11,[23][24][25] Due to the interference of the background electron peaks, the maximum N + change observed in the PFI-PE spectra of Figs. 4(a)-4(d) for the CoC + (X 1 + ; v + = 0) is limited to 3 or 4 and the lowest rotational level identified is N + = 2 from N = 6.…”

Section: Resultssupporting

confidence: 89%

Rovibronically selected and resolved two-color laser photoionization and photoelectron study of cobalt carbide cation

et al. 2013

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We have conducted a two-color visible-ultraviolet (VIS-UV) resonance-enhanced laser photoionization efficiency and pulsed field ionization-photoelectron (PFI-PE) study of gaseous cobalt carbide (CoC) near its ionization onset in the total energy range of 61,200-64,510 cm(-1). The cold gaseous CoC sample was prepared by a laser ablation supersonically cooled beam source. By exciting CoC molecules thus generated to single N' rotational levels of the intermediate CoC∗((2)Σ(+); v') state using a VIS dye laser prior to UV laser photoionization, we have obtained N(+) rotationally resolved PFI-PE spectra for the CoC(+)(X(1)Σ(+); v(+) = 0 and 1) ion vibrational bands free from interference by impurity species except Co atoms produced in the ablation source. The rotationally selected and resolved PFI-PE spectra have made possible unambiguous rotational assignments, yielding accurate values for the adiabatic ionization energy of CoC(X(2)Σ(+)), IE(CoC) = 62,384.3 ± 0.6 cm(-1) (7.73467 ± 0.00007 eV), the vibrational frequency ωe (+) = 985.6 ± 0.6 cm(-1), the anharmonicity constant ωe (+)χe (+) = 6.3 ± 0.6 cm(-1), the rotational constants (Be (+) = 0.7196 ± 0.0005 cm(-1), αe (+) = 0.0056 ± 0.0008 cm(-1)), and the equilibrium bond length re (+) = 1.534 Å for CoC(+)(X(1)Σ(+)). The observation of the N(+) = 0 level in the PFI-PE measurement indicates that the CoC(+) ground state is of (1)Σ(+) symmetry. Large ΔN(+) = N(+) - N' changes up to 6 are observed for the photoionization transitions CoC(+)(X(1)Σ(+); v(+) = 0-2; N(+)) ← CoC∗((2)Σ(+); v'; N' = 6, 7, 8, and 9). The highly precise energetic and spectroscopic data obtained in the present study have served as a benchmark for testing theoretical predictions based on state-of-the-art ab initio quantum calculations at the CCSDTQ∕CBS level of theory as presented in the companion article.

“…Table II. The previous rotationally resolved state-to-state PFI-PE studies of CH 3 I/CH 3 I + , 27 CH 3 Br/CH 3 Br + , 28 FeC/FeC + , 1 NiC/NiC + , 2 CoC/CoC + , 3 TiO/TiO + , 10 VN/VN + , 11 VCH/VCH + , 4 and NbC/NbC +12 show that rotational photoionization transition depends on | N + | = | N + − J | with the minimum | N + | transition having the maximum intensity. Furthermore, the intensity of rotational transition was found to decrease as | N + | increases.…”

Section: Resultsmentioning

confidence: 90%

Rotationally resolved state-to-state photoionization and photoelectron study of titanium carbide and its cation (TiC/TiC+)

et al. 2014

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Titanium carbide and its cation (TiC/TiC(+)) have been investigated by the two-color visible (VIS)-ultraviolet (UV) resonance-enhanced photoionization and pulsed field ionization-photoelectron (PFI-PE) methods. Two visible excitation bands for neutral TiC are observed at 16,446 and 16,930 cm(-1). Based on rotational analyses, these bands are assigned as the respective TiC((3)Π1) ← TiC(X(3)Σ(+)) and TiC((3)Σ(+)) ← TiC(X(3)Σ(+)) transition bands. This assignment supports that the electronic configuration and term symmetry for the neutral TiC ground state are …7σ(2)8σ(1)9σ(1)3π(4) (X(3)Σ(+)). The rotational constant and the corresponding bond distance of TiC(X(3)Σ(+); v″ = 0) are determined to be B0″ = 0.6112(10) cm(-1) and r0″ = 1.695(2) Å, respectively. The rotational analyses of the VIS-UV-PFI-PE spectra for the TiC(+)(X; v(+) = 0 and 1) vibrational bands show that the electronic configuration and term symmetry for the ionic TiC(+) ground state are …7σ(2)8σ(1)3π(4) (X(2)Σ(+)) with the v(+) = 0 → 1 vibrational spacing of 870.0(8) cm(-1) and the rotational constants of B(e)(+) = 0.6322(28) cm(-1), and α(e)(+) = 0.0085(28) cm(-1). The latter rotational constants yield the equilibrium bond distance of r(e)(+) = 1.667(4) Å for TiC(+)(X(2)Σ(+)). The cleanly rotationally resolved VIS-UV-PFI-PE spectra have also provided a highly precise value of 53 200.2(8) cm(-1) [6.5960(1) eV] for the adiabatic ionization energy (IE) of TiC. This IE(TiC) value along with the known IE(Ti) has made possible the determination of the difference between the 0 K bond dissociation energy (D0) of TiC(+)(X(2)Σ(+)) and that of TiC(X(3)Σ(+)) to be D0(Ti(+)-C) - D0(Ti-C) = 0.2322(2) eV. Similar to previous experimental observations, the present state-to-state PFI-PE study of the photoionization transitions, TiC(+)(X(2)Σ(+); v(+) = 0 and 1, N(+)) ← TiC((3)Π1; v', J'), reveals a strong decreasing trend for the photoionization cross section as |ΔN(+)| = |N(+) - J'| is increased. The maximum |ΔN(+)| change of 7 observed here is also consistent with the previous experimental results for the 3d transition-metal carbides, oxides, and nitrides. However, the VIS-UV-PFI-PE spectra for TiC(+)(X(2)Σ(+); v(+) = 0 and 1, N(+)) are found to display only the negative ΔN(+) (N(+)-J'≤ 0) transitions, indicating that the cross sections for the formation of positive ΔN(+) (N(+)-J' > 0) transitions by both the channel coupling mechanism and direct photoionization are negligibly small.