A femtosecond velocity map imaging study on B -band predissociation in CH3 I. I. the band origin

7 p.; 5 fig.; 1 tab.A femtosecond pump-probe experiment, coupled with velocity map ion imaging, is reported on the second absorption band (B -band) of CH3 I. The measurements provide a detailed picture of real-time B -band predissociation in the band origin at 201.2 nm. Several new data are reported. (i) A value of 1.5±0.1 ps has been obtained for the lifetime of the excited state, consistent within errors with the only other direct measurement of this quantity [A. P. Baronavski and J. C. Owrutsky, J. Chem. Phys. 108, 3445 (1998)]. (ii) It has been possible to measure the angular character of the transition directly through the observation of fragments appearing early with respect to both predissociation lifetime and molecular rotation. (iii) Vibrational activity in CH3 has been found, both in the umbrella (2) and the symmetric stretch (1) modes, with estimates of relative populations. All these findings constitute a challenge and a test for much-wanted high level ab initio and dynamics calculations in this energy region. © 2010 American Institute of Physics.We thank Dr. Alberto García-Vela and Dr. Jesús González Vázquez for fruitful discussions. M.E.C. acknowledges financial support from MICINN Spain through a FPU fellowship. This work has been financed by the Spanish MICINN through Grant No. CTQ2008-02578/BQU, the Consolider program “Science and Applications of Ultrafast Ultraintense Lasers,” Grant No. CSD2007-00013, and by the European Union ITN network “Ultrafast control of quantum systems by strong laser fields—FASTQUAST” Grant No. PITN-GA-2008-214962. This research has been performed within the Unidad Asociada “Química Física Molecular” between Departamento de Química Física of UCM and CSIC. The facilities provided by the Centro de Asistencia a la Investigación de Espectroscopia Multifotónica y de Femtosegundo UCM are gratefully acknowledged