Statistical fragmentation of small neutral carbon clusters

We present a statistical fragmentation study of the ${\mathrm{C}}_5$, ${\mathrm{C}}_7$, and ${\mathrm{C}}_9$ carbon clusters using the Metropolis Monte Carlo and Weisskopf methods. We show that inclusion of several isomeric forms as well as rotational effects is essential to reproduce the experimental observations. We have found that, for cluster excitation energies around $10\mathrm{eV}$, several fragmentation channels are efficiently populated, but the dominant one always corresponds to ${\mathrm{C}}_{n-3}∕{\mathrm{C}}_3$. For high enough excitation energies, we observe first-order phase transitions corresponding to a complete breakup of the cluster.

Figure 1

(Color online) Fragmentation of ${\mathrm{C}}_5$ from MMMC simulations. Channel probabilities as functions of excitation energy.

Figure 2

(Color online) Isomer analysis of the ${\mathrm{C}}_3∕{\mathrm{C}}_2$, ${\mathrm{C}}_3∕\mathrm{C}∕\mathrm{C}$, and ${\mathrm{C}}_2∕{\mathrm{C}}_2∕\mathrm{C}$ channels in ${\mathrm{C}}_5$ fragmentation. Discontinuous lines represent channel probabilities. LS, linear singlet; LT, linear triplet; CS, cyclic singlet; CT, cyclic triplet.

Figure 3

(Color online) Time dependent Weisskopf calculations of ${\mathrm{C}}_5$ fragmentation for (a) $\mathrm{TOF}=2\times {10}^{-7}\mathrm{s}$ and (b) $\mathrm{TOF}=\infty$.

Figure 4

(Color online) MMMC simulation for ${\mathrm{C}}_5$ fragmentation without rotational effects.

Figure 5

(Color online) Fragmentation of ${\mathrm{C}}_7$ from MMMC simulations. Channel probabilities as functions of excitation energy.

Figure 6

(Color online) Isomer analysis of the dominant dissociation channels in ${\mathrm{C}}_7$ fragmentation. Discontinuous lines represent channel probabilities. Labels as defined in Fig. 2.

Figure 7

(Color online) Weisskopf calculations for ${\mathrm{C}}_7$ fragmentation using (a) $\mathrm{TOF}=2\times {10}^{-7}\mathrm{s}$ and (b) $\mathrm{TOF}=\infty$.

Figure 8

(Color online) Fragmentation of ${\mathrm{C}}_9$ from MMMC simulations. Channel probabilities as functions of excitation energy.

Figure 9

(Color online) Isomer analysis of the dominant dissociation channels in ${\mathrm{C}}_9$ fragmentation. Discontinuous lines represent channel probabilities. Labels as defined in Fig. 2.

Figure 10

(Color online) Effective temperature as a function of excitation energy (left $y$ axis). Discontinuous lines represent channel probabilities (right $y$ axis).

Figure 11

(Color online) Branching ratios for deexcitation of ${\mathrm{C}}_5$, ${\mathrm{C}}_7$, and ${\mathrm{C}}_9$ clusters. Full circles: experiment; open squares: convolution of the theoretical branching ratios with the energy distributions given in Ref. 5. For ${\mathrm{C}}_9$, the figure does not include channels leading to five or more fragments because the corresponding ratios are smaller than 1%.