Vibrational Ladder Climbing of Liquid-Phase Carbon Dioxide

The advent of mid-infrared (mid-IR) femtosecond laser technologies has enabled multi-quantum vibrational excitation or vibrational ladder climbing (VLC) and has opened a way to control molecular reactions in the electronic ground state [1]. Recently, we have demonstrated successful driving of liquid-phase molecular dissociation by employing plasmonic near-fields of mid-IR pulses generated on a metal surface [2]. One of the challenging applications of such laser control is for metal-surface reactions. In particular, it has been proposed that metal-catalyzed carbon dioxide reduction reactions
$(\text{CO}_{2}\text{RR})$
, which is an essential pathway to solve global warming, can be promoted by vibrational excitation [3]; however, it has not been demonstrated experimentally. To realize vibrational control of CO
2
RR, it is important to investigate vibrational excitation and the following relaxation dynamics among the higher-lying states. Here we report on successful demonstration of VLC in the anti-symmetric stretch
$(v_{3})$
of liquid-phase CO
2
up to the
$v_{3}=9$
state, which is higher than the activation barrier in metal-catalyzed CO
2
RR, and the observation of the following vibrational relaxation dynamics.