Radiative lifetimes, fluorescence quantum yields and photodissociation of the C2N2 (A1Σu−) and (B1Δu) states: evidence for sterically hindered, triplet mediated crossings to the (X1Σg+) ground state

The Composition and Chemistry of Titan's Atmosphere

In this review I summarize the current state of knowledge about the composition of Titan's atmosphere and our current understanding of the suggested chemistry that leads to that observed composition. I begin with our present knowledge of the atmospheric composition, garnered from a variety of measurements including Cassini-Huygens, the Atacama Large Millimeter/submillimeter Array, and other ground- and space-based telescopes. This review focuses on the typical vertical profiles of gases at low latitudes rather than global and temporal variations. The main body of the review presents a chemical description of how complex molecules are believed to arise from simpler species, considering all known "stable" molecules-those that have been uniquely identified in the neutral atmosphere. The last section of the review is devoted to the gaps in our present knowledge of Titan's chemical composition and how further work may fill those gaps.

Observation of the A1A" state of isocyanogen

The A1A" state of isocyanogen, CNCN, is observed using photofragment fluorescence excitation spectroscopy in a room temperature cell and in a molecular beam. The spectra are highly congested, but progressions that correspond to the Franck-Condon active C-N-C bending vibration in the excited state are evident. Linewidth measurements indicate that the excited state lifetime is <10 ps. These measurements are consistent with previous ab initio calculations, which predicted a bent excited state with a short lifetime due to predissociation. Although we do not believe that we have observed the origin band of the electronic transition, we place an upper limit of 42,523 cm(-1) on the energy of the excited state zero point level.

Transient laser frequency modulation spectroscopy

Explicitly time-dependent implementations of optical frequency modulation spectroscopy have been recently applied to a wide range of problems in chemical physics. We provide a brief description of the methodology, with an emphasis on its intrinsic advantages for interrogating transient species. Several examples highlight the application of the technique to high-resolution absorption spectra of free radicals, rate measurements for gas-phase reactions, and Doppler spectroscopy of the gas-phase products of photoinitiated reactions.