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Ultrafast absorption of intense x rays by nitrogen molecules
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10.1063/1.4722756
/content/aip/journal/jcp/136/21/10.1063/1.4722756
http://aip.metastore.ingenta.com/content/aip/journal/jcp/136/21/10.1063/1.4722756

Figures

Image of FIG. 1.
FIG. 1.

Classification of key types of core holes in N2 in the localized core hole picture:12,13 (a) a singly-occupied spatial core orbital on one of the atoms of N2: a single core hole (SCH); (b) a fully-depleted spatial core orbital on one N atom: a double core hole (DCH) on a single site (ssDCH); and (c) a singly-occupied spatial core orbital on both N atoms: a DCH on two sites (tsDCH).

Image of FIG. 2.
FIG. 2.

An N atom after irradiation by x rays of constant spatial beam profile with a photon fluence (photon flux integrated over all times) of 8 × 1011  μm−2 and a Gaussian temporal shape (7) with FWHM duration of 2 fs at varying photon energy ωX. (a) Probabilities P j X) from Eq. (4) to find an N atom in specific charge states: neutral (black), singly (red), doubly (green), triply (blue), quadruply (magenta), quintuply (cyan), sextuply (purple), and septuply (orange). (b) Average charge state from Eq. (6).

Image of FIG. 3.
FIG. 3.

Ion yields of (a) an N atom and (b) an N2 molecule irradiated by x rays of a FWHM duration of 280 fs and a photon energy of 1100 eV. In (a), we show theoretical results from the single atom model of Sec. III for the x-ray flux (9). We assume that only 31% of the nominal pulse energy of 0.26 mJ are actually available in the LCLS experiment (Table I). In (b), we show experimental data for an N2 molecule. The comparison of atomic Y j with molecular ion yields for nitrogen clearly demonstrates the impact of molecular processes during and after the interaction with the x rays.

Image of FIG. 4.
FIG. 4.

Average charge state from N2 subject to LCLS x-ray pulses of varying FWHM duration. We show deduced from the experimental ion yields of N2 (Fig. 5) for the nominal pulse durations 4, 7, 80, and 280 fs, alongside our calculations; the points are connected by interpolation. Specifically, we plot the experimental as black circles, from a single N atom as red squares (Sec. III), from the symmetric-sharing model as green diamonds (Sec. IV A), and from the fragmentation-matrix model (Sec. IV B) as blue triangles. See Table I for further LCLS pulse parameters.

Image of FIG. 5.
FIG. 5.

Molecular ion yields of N2 subject to LCLS x-ray pulses of varying duration: (a) 4 fs, (b) 7 fs, (c) 80 fs, and (d) 280 fs. Experimental are given by the blue bars and theoretical from the fragmentation-matrix model (Sec. IV B) by the red bars. See Table I for further LCLS pulse parameters.

Image of FIG. 6.
FIG. 6.

The probabilities to find N2 during the x-ray pulse in its ground state is given by the black lines; the red lines are the probability for a SCH; the green and blue lines stand for the probability to find a tsDCH and a ssDCH, respectively; the PAPs are indicated by magenta lines. Probabilities are determined for (a) a Gaussian short pulse (7) of a FWHM duration of 4 fs and (b) a Gaussian long pulse of a FWHM duration of 280 fs. See Table I for further LCLS pulse parameters.

Tables

Generic image for table
Table I.

Fragmentation constants for the most probable channels for the four pulse durations. Here, f {0, 2} = 0.74 in all cases [Eq. X]. The LCLS FWHM pulse duration is τX [Eq. (7)], the LCLS photon energy is 1100 eV, and the actually available pulse energy in the LCLS experiment is E P. A nominal pulse energy of 0.15 mJ is specified for 4 fs pulses and 0.26 mJ for the remaining three pulse durations.

Generic image for table
Table II.

Ratios to find SCH decay, the first tsDCH decay, the first ssDCH decay, and a PAPA process after averaging over a varying numbers of SASE pulses and from a Gaussian pulse (7) with a FWHM duration of τX. The ratios are probabilities from volume averaging (8) which are renormalized to the sum of the probabilities for (the first) decay of SCHs, tsDCHs, and ssDCHs. See Table I for further LCLS pulse parameters.

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/content/aip/journal/jcp/136/21/10.1063/1.4722756
2012-06-06
2014-04-25
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Ultrafast absorption of intense x rays by nitrogen molecules
http://aip.metastore.ingenta.com/content/aip/journal/jcp/136/21/10.1063/1.4722756
10.1063/1.4722756
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