Vibrational climbing in carboxyhemoglobin by use of stretched infrared pulses.
Résumé
Vibrational ladder climbing using infrared ultrashort laser pulses is an attractive approach for direct control of the nuclear motion of molecules. This technique relies on the use of infrared pulses which need to be negatively chirped in order to take into account the anharmonicity of the addressed molecular vibration [1]. Vibrational climbing has been demonstrated previously in different systems such as W(CO)6 [2], NO [3] and Cr(CO)6 [4], with the demonstration of molecular dissociation in the latter case. We report here on the demonstration of vibrational climbing in a biological system, carboxyhemoglobin (HbCO). The CO vibration is selectively addressed using stretched mid-infrared pulses of energy 2 mJ centered at a wavenumber of 1900 cm-1 with a spectral width of 150 cm-1 (repetition rate 1 kHz). While a positively chirped pulse results in the excitation of the first two vibrational states only, a negatively chirped pulse allows the excitation of states up to v=6. This technique opens a new approach to the excitation of hemoproteins, using infrared instead of UV pulses.