Molecular frame transient absorption spectroscopy of molecules in the VUV regime*

We describe an experiment and results for the impulsive alignment and transient absorption spectroscopy of molecular samples in the vacuum ultraviolet (VUV) regime. A near-infrared (NIR) femtosecond laser at a central wavelength of 800 nm is split into a drive beam used to generate VUV pulses using high harmonic generation (HHG) in Argon, and an alignment pump beam in order to excite a rotational wave-packet in the molecular sample. Specially coated mirrors are used to select 160 nm (5th harmonic) light for the transient absorption spectroscopy of pre-aligned gas-phase molecules. We observe two distinct electronic states in CO₂ that have different symmetries and correspond to parallel and perpendicular transitions. We extract the dipole moments for these transitions and obtain the molecular frame absorption signal. We also discuss progress towards electric-field-resolved measurements of VUV-excited targets.