Fragmentation of endohedral fullerene $\mathrm{H}{\mathrm{o}}_3\mathrm{N}@{\mathrm{C}}_{80}$ in an intense femtosecond near-infrared laser field

The fragmentation of gas phase endohedral fullerene, $\mathrm{H}{\mathrm{o}}_3\mathrm{N}@{\mathrm{C}}_{80}$, was investigated using femtosecond near-infrared laser pulses with an ion velocity map imaging spectrometer. We observed that $\mathrm{H}{\mathrm{o}}^{+}$ abundance associated with carbon cage opening dominates at an intensity of $1.1\times {10}^{14}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$. As the intensity increases, the $\mathrm{H}{\mathrm{o}}^{+}$ yield associated with multifragmentation of the carbon cage exceeds the prominence of $\mathrm{H}{\mathrm{o}}^{+}$ associated with the gentler carbon cage opening. Moreover, the power law dependence of $\mathrm{H}{\mathrm{o}}^{+}$ on laser intensity indicates that the transition of the most likely fragmentation mechanisms occurs around $2.0\times {10}^{14}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$.

Figure 1

Mass/charge ($m/q$) spectra of $\mathrm{H}{\mathrm{o}}_3\mathrm{N}@{\mathrm{C}}_{80}$ at a laser intensity of $4\times {10}^{14}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$. (a) Overall $m/q$ spectrum. The spectrum for $m/q>220$ has been multiplied by 5. (b) Zoomed-in spectrum displaying peaks between the singly and doubly charged parent ions. In this panel, $38\le n\le 40$ for $\mathrm{H}{\mathrm{o}}_3\mathrm{N}@{\mathrm{C}}_{2n}^{+}$, $37\le n\le 40$ for $\mathrm{H}{\mathrm{o}}_3\mathrm{N}@{\mathrm{C}}_{2n}^{2+}$, and $31\le n\le 37$ for $C_{2n}^{+}$. (c) Spectrum displaying peaks between the doubly and quadruply charged parent ions. In this panel, $37\le n\le 40$ for $\mathrm{H}{\mathrm{o}}_3\mathrm{N}@C_{2n}^{2+}$, $36\le n\le 40$ for $\mathrm{H}{\mathrm{o}}_3\mathrm{N}@C_{2n}^{3+}$, and $39\le n\le 40\mathrm{H}{\mathrm{o}}_3\mathrm{N}@{\mathrm{C}}_{2n}^{4+}$. Note that the detection efficiency of the detector is not taken into account.

Figure 2

Fragment ions correlated with $\mathrm{H}{\mathrm{o}}^{+}$ from $\mathrm{H}{\mathrm{o}}_3\mathrm{N}@{\mathrm{C}}_{80}$ molecules produced in a $4\times {10}^{14}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$ laser field using the covariance mapping technique. (a) Spectrum showing low $m/q$ range for atomic and molecular carbon ions, $\mathrm{H}{\mathrm{o}}^{+}$, and Ho-containing ions. (b) Spectrum showing mid $m/q$ for heavy molecular carbon ion fragments and Ho-containing ion fragments. (c) Spectrum showing high $m/q$ for the heavy fullerene ion fragments, ${\mathrm{N}}_m{\mathrm{C}}_{2n-m}^{+}$ ($58\le 2n\le 74$), $N_m{C}_{2n-m}^{2+}$ ($52\le 2n\le 70$), $\mathrm{Ho}{\mathrm{N}}_m{\mathrm{C}}_{2n-m}^{+}$ ($70\le 2n\le 78$), and $\mathrm{Ho}{\mathrm{N}}_m{\mathrm{C}}_{2n-m}^{2+}$ ($68\le 2n\le 78$), with $m=0,1$.

Figure 3

KED of $\mathrm{H}{\mathrm{o}}^{+}$ from $\mathrm{H}{\mathrm{o}}_3\mathrm{N}@{\mathrm{C}}_{80}$ at the laser intensity of $4\times {10}^{14}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$. The red circles and solid blue line are the experimental KE spectrum and its fitted curve, respectively. The fitted spectrum consists of three components: (1) $\mathrm{H}{\mathrm{o}}^{+}$ emission through Coulomb repulsion associated with carbon cage opening (three green dashed line), (2) $\mathrm{H}{\mathrm{o}}^{+}$ emission through escaping associated with cage opening (magenta dotted line) and (3) $\mathrm{H}{\mathrm{o}}^{+}$ emission associated with carbon cage multifragmentation (black dash-dotted line). The inset shows the VMI image of $\mathrm{H}{\mathrm{o}}^{+}$.

Figure 4

KED of $\mathrm{H}{\mathrm{o}}^{+}$ at different laser intensities (a) $1.1\times {10}^{14}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$, (b) $1.5\times {10}^{14}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$, (c) $2.1\times {10}^{14}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$, (d) $3.3\times {10}^{14}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$, and (e) $5.4\times {10}^{14}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$. The blue dashed lines are the fit for peak V.

Figure 5

(a) The yield of $\mathrm{H}{\mathrm{o}}^{+}$ along with the singly and doubly charged parent molecule (PM) $\mathrm{H}{\mathrm{o}}_3\mathrm{N}@{\mathrm{C}}_{80}$, as a function of laser intensity. (b) Branching ratios between the ion yields of $\mathrm{H}{\mathrm{o}}^{+}$ and the sum of ${\mathrm{HoC}}_2^{+}$ and $\mathrm{HoC}{\mathrm{N}}^{+}$ (black circles), $\mathrm{H}{\mathrm{o}}^{+}$ and $\mathrm{P}{\mathrm{M}}^{+}$ (red diamonds), $\mathrm{H}{\mathrm{o}}^{+}$ and $\mathrm{P}{\mathrm{M}}^{2+}$ (green filled triangles), and between $\mathrm{H}{\mathrm{o}}^{+}$ and ${\mathrm{N}}_m{\mathrm{C}}_{2n-m}^{+}$ ($64<2n<72$, $m=0,1$) (purple unfilled triangle). The results for the parent molecular ions are reproduced from [8].