Crystal field splitting on D↔S transitions of atomic manganese isolated in solid krypton

Narrow excitation features present on the [Ar]3d⁶4s¹ a⁶D(J=9/2–1/2)←[Ar]3d⁵4s² a⁶S1/2 transitions of manganese atoms isolated in solid Kr are analyzed within the framework of weak crystal field splitting. Use of the Wp optical lineshape function allowed identification of multiple zero-phonon lines for individual spin-orbit J states of the a⁶D←a⁶S transition recorded with laser-induced excitation spectroscopy. Excellent agreement exists between the predicted crystal field splitting patterns for the J levels of the a⁶D state isolated in the «red» tetravacancy site of solid Kr. The tetrahedral crystal field of the «red» trapping site splits J>3/2 levels of the a⁶DJ and a⁴D₇/₂ states by approximately 30 cm⁻¹. This report represents the first definitive evidence of crystal field splitting, induced by the weak van der Waals interactions between a neutral metal atom and the rare gas atoms surrounding it in a well defined solid state site

Unveiled optical properties of tetrapyrollic pigments in cryogenic environments

An unexpected phenomenon was revealed in the laser induced fluorescence spectra of free-base (H₂Pc) and zinc (ZnPc) phthalocyanines trapped in rare gas and nitrogen matrices under a moderate increase in the laser intensity. In all matrices the intensity of an emission band near 755 nm increased drastically when pumping the S₁←S₀ transition. This observation was assigned to stimulated emission in a four-level scheme involving a vibronic transition from the lowest electronic state to a vibrational level of the ground state. In the present work, we expose new similar results obtained with porphyrin molecules, i.e. tetra-benzoporphin (TBP). With free-base H₂TBP, stimulated emission was observed in Ar or N₂ matrices, but not in Xe matrices. A possible reason could be a fast inter-system crossing rate due to the heavy atom effect induced by Xe. We also report the observation of persistent burnt spectral holes, although the low efficiency of this process is not competitive with stimulated emission and no decrease of the stimulated emission with time was observed. With ZnTBP, no stimulated emission could be recorded; however the appearance of rather strong phosphorescence was noticed. Similar studies focusing on the stimulated emission phenomenon is that they should allow new insights into site effects and site selectivity

Spectroscopy and photodissociation of chlorine monomers and clusters in argon matrices

Steady-state and time-resolved emission spectroscopy of the A-X system of Cl2 is used to distinguish molecular chlorine isolated as monomers and clusters in solid argon samples. The lifetime of the metastable A' 3-PI-2u state is measured to be an order of magnitude less, when chlorine is present as clusters, than when it is truly isolated. Photodissociation of molecular chlorine clusters was found to be insignificant as monitored by the emission of Ar2Cl at 260 nm. Measurement of the dissociation threshold of molecular chlorine in the 9 eV region as a function of temperature showed little variation. Using spectroscopic data it is concluded that dissociation is occurring by an impulsive mechanism involving curve-crossing from the initially populated Ar+ (Cl2)- charge transfer state to repulsive potentials correlating with ground state atomic chlorine and not via a harpooning mechanism. A simple microscopic model, drawn from experimental data and pairwise addition of ArCl potential terms, is constructed to describe the steps involved in this dissociation process in the solid lattice

The Humbly Grove, Herriard and Hester’s Copse Fields, UK onshore

The Humbly Grove Field has, for the UK, a unique development history. It was discovered as an oilfield in May 1980 and produced as an oilfield until 2000 along with small satellite fields Herriard (developed) and Hester's Copse (not developed). Peak production of 2219 bopd was achieved during July 1986 but, by October 1988, the rate had fallen to around 1000 bopd, a rate that was more or less maintained until October 1995 after which the production fell rapidly. At this point the decision was taken to reconfigure the field as a gas storage facility. Significant renewed pressure depletion occurred between 2000 and 2005, following which first cushion and then storage gas was injected into two reservoirs: the Middle Jurassic, Great Oolite Group and the uppermost Triassic, Rhaetian Westbury Formation. Gas storage operations commenced in 2005 and the reservoirs have undergone cyclical gas injection and gas withdrawal since that date. The cyclical injection of gas and re-pressuring of the Great Oolite reservoir causes mobile oil to be swept towards dedicated oil production wells. This operates effectively as an enhanced oil recovery scheme. The co-produced liquid hydrocarbons provide a valuable secondary income stream for the field