Branch Widths Research Articles

Infrared profile of single molecules adsorbed on ionic substrates: Relaxational mechanism for the homogeneous linewidth

The homogeneous line shape of the infrared spectrum of a single molecule physisorbed on ionic substrates is determined on the basis of a renormalization technique of the total system Hamiltonian. The absorption profile can be written in terms of a limited cumulant series expansion of the dynamical couplings between the optical system formed by the vibration–orientation modes of the molecule, and the bath modes characterized by molecular translations and substrate phonons. The various causes of homogeneous broadening of the lines are studied, implying phase and population relaxations through intramolecular transfers. In this latter case, two situations are considered depending on whether the internal vibration modes of the admolecule are localized or resonant (quasi-resonant) with the substrate phonon modes. These situations are usual for small polyatomic molecules adsorbed on substrates with extended optical phonon bands. An application to the calculation of the Q*, P* and R* branch widths for CO, CO2 and NH3 molecules adsorbed on NaCl(001) and/or MgO(001) is extensively discussed. We show that, at low temperature T≲ 20 K, the homogeneous width is quite negligible and inhomogeneity must be invoked to interpret the measured width. By contrast, for increasing T values (T≳ 50 K), homogeneous broadening increases and contributes significantly (about to 50%) to the measured width for CO and CO2 molecules adsorbed on clean substrates.

Historical record of erect bryozoan growth forms

Information compiled from literature on marine bryozoans suggests that erect taxa have had a limited range of repeatedly evolved growth forms, each with characteristic branch widths or surface morphology, through the nearly 500 Ma history of the phylum. The range of erect growth forms among the Bryozoa has been limited to six (with only rare exceptions) that have co-occurred constantly throughout the history of the phylum. Ciliated tentacles of bryozoan lophophores are located just above the surface of colonies and draw a flow of food-bearing water. Outflow of the filtered water is confined to the space between the tentacles and the colony surface, until some point of escape is reached. In almost all erect bryozoans, lophophores are closely spaced and, in extant species, feed simultaneously. Therefore, for broad surface areas to develop, colony margins must be supplemented by other points of outflow (chimneys), commonly situated on surface disruptions, to keep local volume and velocity within manageable bounds. Presence of chimneys apparently permits branch widths to increase beyond certain size limits into less tightly constrained morphospace, and branch widths have been narrowly limited in the various growth forms except where regularly spaced chimneys can be demonstrated or reasonably inferred. It is hypothesized that the observed limits on form, size and surface morphology are derived primarily from the phylogenetic constraint of byrozoan lophophore size and attendant limitations on flow of filtered water across colony surfaces.

A Combined Photometric/Spectroscopic Study of RR Lyrae Stars in the Globular Cluster Omega Centauri

Most CM diagrams of well observed galactic globular clusters have giant branch widths which are understandable in terms of realistic estimates of random (and systematic) error associated with data acquisition and reduction. Not Omega Centauri. The scatter in (B-V) color among Omega Centauri giant branch stars is considerably greater than that allowed by observational error, differential reddening, or star-to-star mass and/or helium abundance variation (Demarque and Geisler 1963; Woolley 1966; Dickens and Woolley 1967; Rood 1973; Cannon and Stobie 1973; Cannon and Kontizas 1974; Iben 1974; Norris and Bessell 1975; Hesseret al. 1976; 1977). This problem is an old one, but one which has recently received a flurry of attention. Indeed, our next speakers have investigated possible causal relationships between interior mixing and Omega Centauri giant (or subgiant) color. I see from the program that they intend to discuss such things today, so we shall try to avoid those topics as much as possible.