Yields and Time-of-Flight Spectra of Neutral High-Rydberg Fragments at the K Edges of the CO₂ Molecule

Abstract

We have studied the production of neutral fragments in high-Rydberg (HR) states at the C 1s and O 1s edges of the CO2 molecule by performing two kinds of experiments. First, the yields of neutral HR fragments were measured indirectly by ionizing such fragments in a static electric field and by collecting resulting singly charged positive ions as a function of the photon energy. Such measurements reveal not only excitations below the core ionization thresholds but also thresholds for single core-hole and shakeup photoionization. Second, we obtained the mass spectra of neutral HR fragments at selected photon energies by exploiting pulsed field ionization; they show atomic fragments C(HR) and O(HR). We discuss dissociation pathways leading to the production of neutral HR fragments in core excitation and ionization of CO2.

Soft X-ray Induced Production of Neutral Fragments in High-Rydberg States at the O 1s Ionization Threshold of the Water Molecule

“…The calculated positions for the O­(HR) and OH­(HR) peaks, shown with dashed lines in Figure a, agree well with the other features observed in the TOF spectra. The observed position of the O­(HR) peak agreed with that of the corresponding peak in the CO 2 molecule, measured under similar experimental conditions . We also measured a field ionization TOF spectrum at the photon energy of 540.35 eV using a lower pressure of 2.2 × 10 –6 mbar in order to find out whether the prominent oscillations between the H­(HR) and O­(HR) peaks depended on the pressure.…”

“…The observed position of the O(HR) peak agreed with that of the corresponding peak in the CO 2 molecule, measured under similar experimental conditions. 23 We also measured a field ionization TOF spectrum at the photon energy of 540.35 eV using a lower pressure of 2.2 × 10 −6 mbar in order to find out whether the prominent oscillations between the H(HR) and O(HR) peaks depended on the pressure. That low-pressure spectrum is compared in Figure 3b to the uppermost TOF spectrum of panel a; the intensity of the latter spectrum has been divided using the ratios of measuring times and pressures of the vacuum chamber.…”

“…The other spectra have been normalized with respect to the uppermost spectrum using the measured photon flux ratios. The TOF spectra have been mass calibrated by assuming that the peaks at 382 ns and 1.62 μs are due to H(HR) and H 2 O(HR), respectively, and by using the equation given in ref 23. The calculated positions for the O(HR) and OH(HR) peaks, shown with dashed lines in Figure 3a, agree well with the other features observed in the TOF spectra.…”

Vacuum ultraviolet photoionization and ionic fragmentation of the isoxazole molecules

“…The TOF spectrometer (with a 203-mm long drift tube) was oriented parallel to the electric vector of the linearly polarized synchrotron light. In the interaction region, the monochromatic photon beam from the beamline crossed the effusive beam of the sample molecules emanating from a hypodermic needle [31]. The ambient pressure in the experimental chamber was 2.5-8.5×10 -7 mbar during the measurements, but it was estimated to be 10-30 times higher in the interaction region.…”

Neutral Dissociation of Pyridine Evoked by Irradiation of Ionized Atomic and Molecular Hydrogen Beams

“…The interaction of ions with biological molecules in the gas phase leads to ionization, excitation, charge transfer, complex formation, and dissociation processes that produce neutral and ionic products [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. The mass spectrometric methods are developed to probe the charged entities [ 22 , 39 ], as well as to study neutral fragments in high-Rydberg states but without identifying their final states [ 40 , 41 ]. Conversely, excited products can be identified by detecting their emission [ 42 , 43 ].…”