Iron hydride - Laboratory studies and solar identification

Abstract

The spectrum of iron hydride (FeH) has been studied under high resolution in the wavelength range A. Its main features are two regions of complex structure in the blue and green centered at about 4920 A and 5320 A, respectively, and a band degraded to longer wavelengths with a head at 8690.82 A. The identity of the carrier as FeH is established on experimental grounds, and in particular on the basis of the observed deuteride spectrum. The smallness of the vibrational isotope shifts for most of the features indicates that they are 0-0 bands or sequences. Coincidences have been observed between lines in the blue and green regions and weak unidentified solar lines. These possible identifications have been subjected to a critical statistical analysis, and the presence of FeH in both photo sphere and spot has been established with a high degree of certainty. A search for the presence of the 8690.82 A band with the available solar and laboratory data proved negative. An attempt is made to correlate the intensities of the blue and green bands as observed in the photosphere, in sunspots, and in laboratory spectra. The indications are that FeH has a rather low dissociation energy ( 1.0 eV), but that the oscillator strength for the blue and green features may be fairly large ( 0.67). The possibility of observing FeH in the spectra of cooler stars is briefly discussed. Subject headings: laboratory spectra - line identifications - molecular processes - Sun: spectra