Lifetimes of high Rydberg states of methyl halides

The lifetimes of high Rydberg states of the methyl halides CH₃I, CH₃Br and CH₃Cl have been studied. A pulsed dye laser tuned near half the ionization energy was used, with preprogrammed field pulses, and the high Rydberg states of the compounds in selected ranges of n values were ionized after a variable delay. Plots of the electron signal versus delay yielded information about the Rydberg state lifetime. The clearest trend was found for around n = 120–160: the lifetimes of the states decreased by more than an order of magnitude from CH₃I (τ ≈12.3 μs) through CH₃Br to CH₃C1. Within the range studied, the theoretically predicted increase in lifetimes (n ⁵ or n ³) was not found, and in fact the highest group of states studied (with n > 215) exhibited for all three compounds relatively short lifetimes (≈2-3 μs), possibly due to collisional processes.     

The sensitive detection of NO by Faraday modulation spectroscopy with a quantum cascade laser

A spectrometer based on a quantum cascade laser and capable of operating at particular wavelengths in the mid-infrared with very high sensitivity for the detection of open-shell molecules has been developed. It exploits magnetic field modulation in the Faraday rotation configuration. The signals for nitric oxide (NO) that may be observed with this instrument have been studied and their dependence on the J and Ω quantum numbers investigated with a simulation program. It is shown that the Q(3/2) transition of NO in the ²Π_3/2 component at 1875.8 cm^?1 would provide the greatest sensitivity for detection. The experimental observation of the R(21/2) transition of the Ω = 1/2 component gives a detection limit of 41 ppb of NO in air at a pressure of 25 mbar. Detection of NO through the Q(3/2) transition would provide a detection limit of 4 ppb at this pressure.     

Benchmark calculations of some molecular properties of O2, CN and other selected small radicals using the ROHF-CCSD(T) method

The capability of the ROHF-CCSD(T) method in obtaining accurate molecular properties in a defined and controlled way is analysed. Electron affinity, polarizability, and hyperpolarizability of the oxygen molecule in its ground state, electron affinity, electric dipole moment of the CN radical, and some other molecules serve as model cases for obtaining the ‘right result for the right reason’. Most calculated CCSD(T) data were extrapolated to the complete basis set (CBS) limit in order to minimize the basis set dependence of results. Some problems, specific to open shell systems include effects due to the spin adaptation, and details in the selection of the reference orbitals and related selection of denominators in non-iterative triples and other subtleties, which can affect the accuracy of the final ROHF-CCSD(T) results, are investigated.