Fragmentation processes of ionized 5-fluorouracil in the gas phase and within clusters

We have measured mass spectra for positive ions produced from neutral 5-fluorouracil by electron impact at energies from 0 to 100 eV. Fragment ion appearance energies of this (radio-)chemotherapy agent have been determined for the first time and we have identified several new fragment ions of low abundance. The main fragmentations are similar to uracil, involving HNCO loss and subsequent HCN loss, CO loss, or FCCO loss. The features adjacent to these prominent peaks in the mass spectra are attributed to tautomerization preceding the fragmentation and/or the loss of one or two additional hydrogen atoms. A few fragmentions are distinct for 5-fluorouracil compared to uracil, most notably the production of the reactive moiety CF+. Finally, multiphoton ionization mass spectra are compared for 5-fluorouracil from a laser thermal desorption source and from a supersonic expansion source. The detection of a new fragment ion at 114 u in the supersonic expansion experiments provides the first evidence for a clustering effect on the radiation response of 5-fluorouracil. By analogy with previous experiments and calculations on protonated uracil, this is assigned to NH3 loss from protonated 5-fluorouracil

Vibronic Spectra of Molecular Systems

NRC publication: Ye

Resonance Raman Scattering in Molecules with Vibronically Coupled Excited States

NRC publication: Ye

Non-Condon Effects in the X - A Electronic Absorption Band System of Sulphur Dioxide

NRC publication: Ye

Quantitative Interpretation of the Absorption and Emission Spectra of 1,8-diphenyl-1,3,5,7-Octatetraene

Peer reviewed: YesNRC publication: Ye

Theory of Resonance Raman Scattering Beyond the Condon Approximation for a System with Two Modes of Different Symmetry

Peer reviewed: YesNRC publication: Ye

Normal-Coordinate Rotation as a Cause of Missing Bands in Molecular Electronic Spectra. The Case of Magnesium Tetrabenzo Porphine

Peer reviewed: YesNRC publication: Ye

Exactly Solvable Models for Vibronic Coupling in Molecular Spectroscopy. I. Nontotally Symmetric Harmonic Mode

Peer reviewed: YesNRC publication: Ye

Exactly Solvable Models for Vibronic Coupling in Molecular Spectroscopy. II. Totally Symmetric Harmonic Mode

Peer reviewed: YesNRC publication: Ye

Direct observation of electronic relaxation dynamics in adenine via time-resolved photoelectron spectroscopy

We present femtosecond time-resolved photoelectron spectra of adenine in a molecular beam, recorded at pump wavelengths of 250, 267, and 277 nm. This leads to initial excitation of the bright S2(????*). Close to the band origin (277 nm), the lifetime is several picoseconds. Higher vibronic levels (267 and 250 nm excitation) show much shorter lifetimes of t < 50 fs, and we observe strong coupling between S2(????*) and S1(n??*). Rapid internal conversion (t < 50 fs) populates the lower lying S1(n??*) state which has a lifetime of 750 fs. At 267 nm, we found evidence for an additional channel which is consistent with the dissociative S3(????*) state, previously proposed as an ultrafast relaxation pathway from S2(????*).close11311