An investigation of the working conditions of an infra-red spectrometer of the recording type has resulted in techniques of operation which have increased the precision of the measurements attainable and has permitted an appraisal of the magnitudes of the variations in the resulting data which may still be expected. Included in this study is the remeasurement of the fine structure of certain of the absorption bands of CO2, NH3, and H2O. Measured with a grating instrument whose resolution was made to equal that of the prism instrument in each case, these data give 150 sharp absorption lines between 5μ and 15μ suitable for an empirical calibration of great accuracy.

Detachment of heme prosthetic groups from gaseous myoglobin ions has been studied by collision-induced dissociation and infrared multiphoton dissociation in combination with Fourier-transform ion cyclotron resonance mass spectrometry. Multiply charged holomyoglobin ions (hMbn+) were generated by electrospray ionization and transferred to an ion cyclotron resonance cell, where the ions of interest were isolated and fragmented by either collision with Ar atoms or irradiation with 3 mum photons, producing apomyoglobin ions (aMbn+). Both charged heme loss (with [Fe(III)-heme]+ and aMb(n-1)+ as the products) and neutral heme loss (with [Fe(II)-heme] and aMbn+ as the products) were detected concurrently for hMbn+ produced from a myoglobin solution pretreated with reducing reagents. By reference to Ea = 0.9 eV determined by blackbody infrared radiative dissociation for charged heme loss of ferric hMbn+, an activation energy of 1.1 eV was deduced for neutral heme loss of ferrous hMbn+ with n = 9 and 10.