Search

Abstract: As efforts continue to elucidate laser–cluster interactions, we investigated the influence of laser wavelength on ion products. In this study, a pulsed methyl iodide cluster was irradiated with a Nd–YAG nanosecond laser, and the ion products were analyzed using time-of-flight mass spectrometry. Multiple-charge atomic ions of C q+ and I q+(q ⩾2) were observed using 532 and 1064nm laser wavelengths; however, only single-charge atomic and molecular ions appeared at 266 and 355nm. We show that the charge-state distribution for multiple-charge ions is almost independent of laser intensity. A three-stage model was developed to further understand these experimental results: the inverse electron bremsstrahlung heating rate is proportional to the square of laser wavelength, which seems to explain the dependence of multiple-charge ions on the wavelength. [Copyright &y& Elsevier]

Abstract: The photodissociation of n-C7H15Br, near the red wing of the absorption A-band, has been investigated utilizing the velocity mapped ion imaging technique. Both the speed and angular distributions of Br∗(2P1/2) and Br(2P3/2) fragments were determined. The experimental data indicate that the photodissociation in the investigated range originates from adiabatic and non-adiabatic transitions of the three low-lying dissociative electronic states. The fragments kinetic energies and the angular distributions show that about 70% energy is deposited into the internal energy of the fragments. These results can be explained using soft impulsive model. The experiment also shows that the anisotropy parameter for Br∗ is sensitive to the photolysis wavelength. [Copyright &y& Elsevier]

Abstract: The dependences of kinetic energies and peak profiles of multicharged ions of I q+ (q =2–3) and C2+ on the laser intensity have been studied in detail by time-of-flight mass spectrometry, those multicharged ions are produced by irradiation of methyl iodide cluster beam with a nanosecond 532nm Nd-YAG laser. Our experiments show that the kinetic energies released of multicharged ions increase linearly with the laser intensity in the range of 3×109–2×1011 W/cm2. The peaks of multicharged ions are split to forward ions and backward ions, and the ratio of the backward ions to forward ions decreases exponentially with laser intensity. The decreasing of backward ions is probably due to Coulomb scattering by the heavier I+ ions when they turn around through the laser focus point. The linear dependence of kinetic energy of multicharged ions on laser intensity is interpreted by the ionization mechanism, in which the laser induced inverse bremsstrahlung heating of electron is the rate-limiting step. [Copyright &y& Elsevier]

Abstract: A theoretical method to calculate multidimensional Franck–Condon factors including Duschinsky effects is described and used to simulate the photoelectron spectrum of the anion . Geometry optimizations and harmonic vibrational frequency calculations have been performed on the state of SO2 and state of . Franck–Condon analyses and spectral simulation were carried out on the first photoelectron band of . The theoretical spectra obtained by employing CCSD(T)/6-311+G(2d,p) values are in excellent agreement with the experiment. In addition, the equilibrium geometric parameters, r e(OS)=0.1508±0.0005 nm and θ e(O–S–O)=113.5±0.5°, of the state of , are derived by employing an iterative Franck–Condon analysis procedure in the spectral simulation. [Copyright &y& Elsevier]

Abstract: The formation mechanism for multiply charged ions (C q + and O q + (q =2–4)) were investigated using a dual polarity time-of-flight mass spectrometer when diethyl ether clusters interacted with nanosecond laser pulse. The signal intensity of multiply charged ions and electron energy was measured experimentally. It was shown that the intensity of multiply charged ions increased about 50 times when laser intensity increased from 7.6×109 to 7.0×1010 W/cm2, then saturated as laser intensity increased further. It is interesting that the evolution of the mean value of electron energy was same to that of multiply charged ions. The theoretical calculation showed the ionization potential of atomic ions could be significantly decreased due to the effect of Coulomb screening especially at low laser intensity. It indicated that the electron ionization combined with Coulomb screening effect could explain the production of multiply charged ions in nanosecond laser field. [ABSTRACT FROM AUTHOR]

Abstract: The photoionization of methyl iodide beam seeded in argon and helium is studied by time-of-flight mass spectrometry using a 25 ns, 532 nm Nd-YAG laser with intensities in the range of 2×1010–2×1011 W/cm2. Multiply charged ions of Iq+ (q=2–3) and C2+ with tens of eV kinetic energies have been observed when laser interacts with the middle part of the pulsed molecular beam, whose peak profiles are independent on the laser polarization directions. Strong evidences show that these ions are coming from the Coulomb explosion of multiply charged CH3I clusters, and laser induced inverse bremsstrahlung absorption of caged electrons plays a key role in the formation of multiply charged ions. [Copyright &y& Elsevier]

A theoretical method to calculate multidimensional Franck–Condon factors including Duschinsky effects is described and used to simulate the photoelectron spectra of HNO− and DNO− radicals. Geometry optimization and harmonic vibrational frequency calculations have been performed on the X˜ 1A′ and a˜ 3A″ states of HNO/DNO and X˜ 2A″ state of HNO−/DNO−. The theoretical spectra obtained by employing B3LYP/6-311+G(2d,p) values are in excellent agreement with the observed ones. In addition, the equilibrium geometry parameters, R(NO)=0.1335±0.0005 nm, ∠(HNO)=106.3°±0.5°, of the X˜ 2A″ state of HNO−/DNO− are derived by employing an iterative Franck–Condon analysis procedure in the spectral simulation. [Copyright &y& Elsevier]