Photofragmentation Of Molecules Research Articles

Ionization and Fragmentation of DCOOD Induced by Synchrotron Radiation at the Oxygen 1s Edge: The Role of Dimer Formation.

The ionization and photofragmentation of molecules in the core region has been widely investigated for monomers and dimers of organic molecules in the gas phase. In this study, we used synchrotron radiation to excite electrons of the oxygen K-edge in an effusive molecular beam of doubly deuterated formic acid. We used time-of-flight mass spectrometry and employed the spectroscopic techniques photoelectron-photoion coincidence and photoelectron photoion-photoion coincidence to obtain spectra of single and double coincidences at different pressures. Our results indicate the presence of ions and ion pairs that have charge-to-mass ratio higher than the monomer DCOOD, as the (DCOOD)·D(+), and pairs (DCO(+), DCO(+)) and (CO(+), DCO(+)). Comparing the spectra obtained for different pressures we can ascertain that these ions are formed by the fragmentation of DCOOD dimers.

Floquet representation of absolute phase and pulse-shape effects on laser-driven molecular photodissociation

Using a recent reformulation of Floquet theory [S. Gu\'erin and H. R. Jauslin, Adv. Chem. Phys. 125, 1 (2003)], we discuss the dynamical role of the absolute phase in the photofragmentation of molecules subjected to laser pulses. We show how the dependence of Floquet states on an absolute phase is related to the complexity of the dressed molecular scheme and to the multiphoton character of the molecular dynamics. The general theory is applied to the study of the photodissociation of $\mathrm{H}_{2}{}^{+}$ in a $400\text{\penalty1000-\hskip0pt}\mathrm{nm}$ periodic laser pulse, repeated with a frequency lying in the IR. The dependence of the dynamics on the phase of the pulse envelope is highlighted through an effect previously called dynamical dissociation quenching (DDQ) [F. Ch\^ateauneuf et al., J. Chem. Phys. 108, 3974 (1998)] and through photofragment kinetic energy spectra. These spectra allow us to map out the Floquet content of the dynamics---i.e., its multiphoton character both with respect to the carrier-wave frequency, which gives rise to the usual bond-softening mechanism, and with respect to the pulse modulation frequency in the IR. The synchronization of this pulse modulation with the wave packet motion governs the DDQ effect in this uv-visible pulsed excitation case.

Metal Emissions Monitoring Using Excimer Laser Fragmentation-Fluorescence Spectroscopy

Abstract Photofragmentation of molecules using an excimer laser with subsequent detection of fluorescence from metal atoms formed in excited states is a viable detection strategy for many metal species. Excimer laser fragmentation-fluorescence spectroscopy (ELFFS) can provide continuous, real-lime monitoring information for metals which evolve from a variety of high-temperature processes, including combustion, Here we apply ELFFS to lead, manganese, nickel and chromium species in the postflame gases of a laboratory burner. Using a 193-nm argon fluoride laser we obtain quantitative relationships between signal strength and concentration in hot combustion products for metals injected into a flame; representative spectra are shown. The effects of quenching environment and laser power on the signal are discussed. The ELFFS technique is sensitive, providing ppb detection limits for these metals in a one-second measurement time.

Laser resonance photoionization spectroscopy of molecules

This review concerns the important problem of resonance interaction of laser radiation with polyatomic molecules via intermediate electronic excited states. The relation between the photoionization yield and photofragmentation of molecules and the spectroscopic and physicochemical properties of molecules in excited electronic states is discussed. The application of resonance laser photoionization to ultrasensitive (down to single molecules) detection of polyatomic molecules is examined.