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The zeolites are a group of minerals whose complex and beautiful atomic structures are formed by different arrangements of a very simple building block- a group of four oxygen atoms forming a tetrahedron, with a silicon or aluminium atom at the centre. Each oxygen atom belongs to two tetrahedra, so the structure can be viewed as a network of tetrahedra linked at the corners.

Zeolites have found widespread applications in chemical industry, particularly as catalysts. Their chemical properties depend on the shape of the pores and channels that run through the structure, containing water molecules, ions and even small organic molecules. More than a hundred different frameworks are known to exist in natural minerals or have been synthesised by chemists.

A fundamental geometric question is whether it is possible for the tetrahedra of the framework to exist in an undistorted, geometrically ideal form, or whether distortions are inevitably caused by the linking together of the tetrahedral units to form the structure. A new study links this question to the compression behaviour of zeolites in the analcime group. Four different structures display a common behaviour: they exist in a high-symmetry form at low pressures when the tetrahedra can exist without distortions, but transform to low-symmetry forms under pressure when distortions become inevitable. A deeper understanding of the rules governing the formation of zeolite structures may one day allow us to synthesise structures with specific properties on demand. New insights into the physics and geometry of frameworks are an important step in this direction.

A new high sensitivity technique is developed by extending the broad-band absorption spectroscopy to the vacuum ultraviolet (VUV) spectral region. It is well adapted for the detection and density measurement of closed-shell molecules that have strong electronic transitions in the 110-200 nm range. Among them, molecules such as Cl₂, HBr, BrCl, Br₂, HCl, BCl₃, SiCl₄, SiF₄, CCl₄, SF₆, CH₂F₂ and O₂, used in the microelectronics industry for etching or deposition processes, are of prime interest. In our system, the light of a deuterium lamp crosses a 50 cm diameter industrial etch reactor containing the gas of interest. The transmitted light is recorded with a 20 cm focal length VUV scanning spectrometer backed with a photomultiplier tube (PMT). The attached figure shows the absorbance at three pressures of the HBr gas, which is used in silicon gate etching processes. Peaks at 137, 143 and 150 nm, which show a non-linear, but very strong absorbance, correspond to transitions to Rydberg states of the molecule and can be used for the detection of very small HBr densities. In our present experiment, an absorption rate of 2%, corresponding to about 0.03 mTorr of HBr, can be easily detected on the 143 nm absorption peak. Replacing the PMT detector by a VUV sensitive CCD camera, would permit to reach the same signal to noise ratio with a few seconds acquisition time. For HBr pressures in the 1 to 100 mTorr range, the continuum part of the absorption spectrum (160-200 nm), which shows a weak but linear absorbance can be used. The technique is applied to monitor in Cl2-HBr mixture the dissociation rate of HBr and the amount of Br2 molecule formation at different plasma conditions.

Since Proca's prediction in 1936 that the rest mass of the photon, m_γ, may not be zero, there have been several searches for evidence for a possible finite photon mass. In fact, for even a very small value of m_γ, fascinating physical implications arise such as breakdowns of Coulomb's law, wavelength dependence of the speed of light in free space, existence of longitudinal electromagnetic waves, presence of an additional Yukawa potential for magnetic dipole fields, and effects that a photon mass may have during early-universe inflation and the resulting magnetic fields on a cosmological scale.

Traditionally, limits on m_γ of < 10-49g have been obtained by means of classical approaches, such as searches for departures from Coulomb's law. What happens if we instead exploit quantum approaches? Could better limits be achieved? This is the novel objective of the present work, in which quantum physics is applied to the photon mass question. We first examine the implications that the Aharonov-Bohm class of quantum effects (Figure) have on searches for m_γ, and then move on to explore the quantum electrodynamics scenario with an approach that employs measurements of the electron's g-factor. Within the quantum framework, we show that competitive new lower limits on the photon mass may reach the range 10^-54 < m_γ < 10^-53g. We provide an assessment of the state of the art in these areas and a prognosis for future work.