Electronic absorption spectrum of copper formate tetrahydrate

Single crystals of copper formate tetrahydrate were grown at room temperature. Spectra in the near infrared at room temperature and in the visible at room and liquid air temperatures were recorded on a Unicam SP-700 spectrophotometer and Hilger medium quartz spectrograph respectively. The observed absorption bands have been attributed to an ion of Cu²⁺ in tetragonal symmetry with ²B_1g as the ground state. Taking into consideration the spin—orbit coupling associated with the tetragonal field, a successful interpretation of all the observed bands has been made. The band observed in the near infrared at 11000 cm^?1 has been indentified with a vibrational overtone mode of CO₂. The crystal parameters derived are Dq = ?1380 cm^?1, Ds = ?1950 cm^?1, Dt = ?205 cm^?1 and λ = ?830 cm^?1.