Photodissociation Dynamics of Astrophysically Relevant Propyl Derivatives (C₃H₇X; X = CN, OH, HCO) at 157 nm Exploiting an Ultracompact Velocity Map Imaging Spectrometer: The (Iso)Propyl Channel

The photodissociation dynamics of astrophysically relevant propyl derivatives (C₃H₇X; X = CN, OH, HCO) at 157 nm exploiting an ultracompact velocity map imaging (UVMIS) setup has been reported. The successful operation of UVMIS allowed the exploration of the 157 nm photodissociation of six (iso)propyl systems─n/i-propyl cyanide (C₃H₇CN), n/i-propyl alcohol (C₃H₇OH), and (iso)butanal (C₃H₇CHO)─to explore the C₃H₇loss channel. The distinct center-of-mass translational energy distributions for the i-C₃H₇X (X= CN, OH, HCO) could be explained through preferential excitation of the low frequency C-H bending modes of the formyl moiety compared to the higher frequency stretching of the cyano and hydroxy moieties. Although the ionization energy of the n-C₃H₇radical exceeds the energy of a 157 nm photon, C₃H₇⁺was observed in the n-C₃H₇X (X = CN, OH, HCO) systems as a result of photoionization of vibrationally "hot" n-C₃H₇fragments, photoionization of i-C₃H₇after a hydrogen shift in vibrationally "hot" n-C₃H₇radicals, and/or two-photon ionization. Our experiments reveal that at least the isopropyl radical (i-C₃H₇) and possibly the normal propyl radical (n-C₃H₇) should be present in the interstellar medium and hence searched for by radio telescopes.