A schematic for IR-HF is shown below. Molecules are excited to the v=1 ground state vibrational level of one of the conformations in a region of the expansion that allows for collisional recooling back to the ground state. Since the energy of a single IR photon is greater than most isomerization barriers, some of the molecules will isomerize. Thus when we probe the new conformational distribution we will see gains in the signal for the other conformations and a depletion in the signal for the conformation initially excited.

SEP-Population Transfer Spectroscopy (SEP-PTS) and SEP-Hole Filling (SEP-HF)

SEP-PTS and SEP-HF allows us to experimentally measure barriers to conformational isomerization. A schematic is shown below, along with an animation. The first step in this experiment is the pump-dump SEP step. The pump-dump step occurs in a region of the jet where the molecules may still undergo collisions. The molecules have been prepared with a known amount of energy. If this energy is enough for the molecule to pass over an isomerization barrier, then the molecule may undergo conformational isomerization. Regardless of whether the molecule has enough energy to isomerize, it is collisionally cooled back to the zero point level of the ground state. The final step in the experiment is to probe the new conformational distribution in the collision free region of the jet. If we scan the dump laser and keep the other lasers fixed we refer to the experiment as SEP-PTS, but if we scan the probe (while keeping the others fixed) we call the experiment SEP-HF.