Spectroscopy of forbidden transitions in ions of astrophysical interest E. Charro * , I. Martı ´n Departamento de Quı ´mica Fı ´sica, Universidad de Valladolid, 47011 Valladolid, Spain Accepted 11 February 2002 Abstract The spectroscopic study of forbidden transitions in ions of astrophysical interest has been performed using an extension of the well-established relativistic quantum defect orbital (RQDO) method. The method has so far proved to be a very useful tool for predicting a large body of electron transition probabilities, and other related properties. The RQDO method has been applied to the study of E2 transitions in the spectra of ions relevant in astrophysics, such as Ti XII, Fe XVI, Co XVII and Ni XVIII. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Spectroscopy study; Atomic spectra and related properties; Relativistic quantum defect orbital Resumen El estudio espectrosco ´pico de transiciones prohibidas en iones de intere ´s astrofı ´sico ha sido realizado usando una extensio ´n reciente del metodo Relativista de Orbitales de Defecto Cua ´ntico (RQDO). Este me ´todo, extensamente probado con anterioridad, resulta ser una herramienta muy u ´til a la hora de predecir un gran nu ´mero de probabilidades de transicio ´n y otras propiedades con ellas relacionadas. En este trabajo, se ha aplicado el me ´todo RQDO al estudio de transiciones de tipo E2 en los espectros de iones que son relevantes en el campo de la astrofı ´sica, tales como Ti XII, Fe XVI, Co XVII y Ni XVIII. q 2002 Elsevier Science B.V. All rights reserved. 1. Introduction The prediction of atomic spectra, using different theoretical methods, is an area of continuous development. The most thoroughly studied atomic transitions have been those, which take place through the electric dipole or E1 mechanism, as these are usually responsible for the strongest lines in atomic spectra. The calculation of transition probabilities, expressed as S-, f- or A-values, is a subject of considerable interest in many fields. For example, these quantities are very important in astrophysical studies as they play an important role in the determination of atomic abundances. However, it is now realized that under conditions which prevail in astrophysical and low-density laboratory tokamak 0166-1280/03/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S0166-1280(02)00535-3 Journal of Molecular Structure (Theochem) 621 (2003) 75–85 www.elsevier.com/locate/theochem * Corresponding author. Tel.: þ34-983-423272; fax: þ 34-983- 423013. E-mail address: elena@cpd.uva.es (E. Charro), lmnieto@ wamba.cpd.uva.es (E. Charro).