= Nitrogen dissociation threshold from fragment images
A <molecular nitrogen> experiment used a $0.5\,\mathrm{mm}$ pulsed nozzle and two skimmers. A $5\,\mathrm{cm}$ tube raised the rotational <temperature>. Opposed vacuum-ultraviolet <laser> pulses excited selected molecular levels and, about $10\,\mathrm{ns}$ later, selectively ionized excited <nitrogen> fragments. A <microchannel plate detector>, phosphor screen and camera recorded radii.<Accurate measurements of the bond dissociation energies of 14N2, 14N15N and 15N2 by Liya Lu and others>[Lu, Jiang and Gao, §2, printed manuscript pp. 2–3: nozzle, tube, pump/probe and imaging readout]{ref}
The measured squared radii were fitted against molecular excitation <energies>, referenced to the parent <ground state>:
$$
E_j=D_{0,\rm channel}+\kappa R_j^2.
$$
The intercept at zero radius gave the excited-product threshold; the fitted slope absorbed the detector scale. A wavemeter monitored the excitation source; scanning the probe covered the recoil <Doppler shift>. Subtracting the atomic excitation <energies> converted the intercept to ground-product $D_0$.<Accurate measurements of the bond dissociation energies of 14N2, 14N15N and 15N2 by Liya Lu and others>[§1: image-radius equation; §2: wavemeter and probe scan; §3 and Figure 4: fits; §4: atomic excitation correction]{ref}
An apertured grounded plate and detector timing rejected faster competing channels. Selecting fragment electronic states distinguished nearby thresholds. Agreement of $D_e$ across <isotopes> after <zero-point energy> correction tested consistency. The method still requires correctly assigned levels, adequate near-threshold signal and stable imaging; a signal drop alone can reflect another channel or a barrier.<Accurate measurements of the bond dissociation energies of 14N2, 14N15N and 15N2 by Liya Lu and others>[§2: shielding plate and timing; §3: state-selected channels; §4 and Table 2: isotope consistency and limitations]{ref}
This measurement determines a state-resolved <ground-state dissociation energy>. Obtaining a finite-<temperature> <bond-dissociation enthalpy> requires the thermal increments above; obtaining a <bond potential-well depth> requires the <zero-point energy> correction. The three quantities describe different starting conditions for the same specified separation.
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