Transient chemical forms of molecular ions emitted from a graphite surface byN2laser excitation

Laser-induced molecular-ion emission from a graphite crystal has been investigated with spectrometers of the time-of-flight (TOF) type and of quadrupole mass (QM) one. Both types of measurements show mass spectra entirely different from each other. The difference comes from the fact that the TOF method identifies the mass-to-charge ratio of emitted ions within a period less than 1 μs after emission, whereas the QM measures the ratio in more than 20 μs. Our TOF detects ions of the molecular form ${{\mathrm{C}}_{3i}}^{2+}$ $(i=1,2,3,\dots )$ under positive field acceleration as well as ${{\mathrm{C}}_{3i}}^{2-}$ under a negative one. A separate measurement by a 127° cylindrical electrostatic energy analyzer determines the average time required for ${\mathrm{C}}_3^{2+}$ ions to disintegrate into ${C_1}^{+}$ from the plot of transit time through the analyzer versus the deflecting field. This transformation time is estimated to be 9±1.6 μs under the pulsed-laser-field intensity of 10 to 100 MW/${\mathrm{cm}}^2$ and its pulse width of 10 ns.