Jr. Srinivasan et al., VELOCITY DISTRIBUTIONS FOR A LASER-VAPORIZED, ANTHRACENE-LABELED NUCLEOTIDE, Journal of physical chemistry, 99(35), 1995, pp. 13272-13279
We report the laser vaporization and multiphoton ionization of two ant
hracene-labeled molecules, N-(6-hydroxyhexyl)-3-(9-anthryl)propionamid
e and an anthracene-linked deoxythymine monophosphate. Laser vaporizat
ion of the anthracene-containing molecules was performed by directing,
a high-intensity pulse (30-300 mJ/cm(2), 2.5 ns) of 532 nm laser ligh
t into a thin film of rhodamine 6G (Rh 6G) containing nanomolar quanti
ties of the sample. Resonance-enhanced multiphoton ionization was used
to selectively ionize the anthracene moiety in each molecule after va
porization. The S-0-S-1 transition of the anthracene molecule at 361 n
m was used to excite the molecules, and ionization from this intermedi
ate state was achieved using a 308 nm photon. The ionized products wer
e detected and analyzed by mass spectrometry. The time-of-arrival meas
urements for the laser-vaporized molecules correspond to a bimodal vel
ocity distribution, composed of a thermal component and a hyperthermal
component showing substantial translational energy cooling. The distr
ibutions for the anthracene-labeled molecules reveal lower most probab
le velocities than those for the Rh 6G. A photochemical laser ejection
model is proposed to-account for the energetic nonthermal velocity di
stributions measured.