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

Abstract

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 C3H7 loss 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-C3H7 radical 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-C3H7 fragments, photoionization of i-C3H7 after a hydrogen shift in vibrationally “hot” n-C3H7 radicals, 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.

Combustion in a Sustainable World: From Molecules to Processes

“…Discrepancies between state-of-the-art theory and experiments have also been noted in the temperature dependence of the self-reaction of HO 2 + HO 2 leading to H 2 O 2 + O 2 ; these could be resolved using a multiscale informatics approach that takes into account experimental raw data and, compared to previous work, includes the formation of a HOOOOH intermediate . Experimental investigations with laser and synchrotron-based techniques have led to an improved understanding of several reaction systems of combustion and astrophysical interest, including the CH + H 2 ⇌ 3 CH 2 + H reaction, and the photodissociation dynamics of propyl derivatives . Such techniques also support the identification of transient reaction intermediates, such as phenoxy radical, which is a key intermediate in benzene oxidation and biomass conversion .…”

“…2 Discrepancies between state-of-the-art theory and experiments have also been noted in the temperature dependence of the self-reaction of HO 4 and the photodissociation dynamics of propyl derivatives. 5 Such techniques also support the identification of transient reaction intermediates, such as phenoxy radical, which is a key intermediate in benzene oxidation and biomass conversion. 6 The well resolved high-resolution mass-selected threshold photoionization spectrum from Fernholz et al 6 provides a means for identifying this species in subsequent combustion kinetics studies.…”

Virtual Issue on Photodissociation: From Fundamental Dynamics and Spectroscopy to Photochemistry in Planetary Atmospheres and in Space

“…Experimental strategies to study the intricate mechanisms of photodissociation often focus on isolated gas-phase molecules to avoid the complexities introduced by a surrounding environment such as a solvent. The preferred design for experiments of this type uses a molecular beam of internally cooled molecules, intersected by two pulsed laser beams to excite the molecules and probe the consequences of the excitation, and information-rich detection methods such as velocity map imaging (VMI), ,,,− H Rydberg atom photofragment translational spectroscopy (HRA PTS), , or photoelectron spectroscopy. , These approaches can be divided into two broad categories. Ultrafast time-resolved methods use femtosecond laser spectroscopy methods to observe the real-time changes in molecular structures and electronic states following the initial photoexcitation step .…”

“…Laboratory study of these processes requires a VUV source with sufficient flux to make the desired experimental measurements. Suitable options include excimer lasers, four-wave mixing up-conversion of UV laser light, or for greatest choice of wavelength, a VUV free electron laser …”

“…Indeed, most of the oxidation pathways for biogenic and anthropogenic volatile organic compounds in the troposphere are initiated by these or other photodissociation processes. Shorter wavelength vacuum UV radiation does not penetrate to low altitudes in the Earth’s atmosphere, but VUV light emitted by the sun and other stars does play a role in the photochemistry of planetary atmospheres, cold molecular clouds, and other regions of interstellar space . Closer to home, chemists exploit photodissociation via the technique of flash photolysis to create reactive intermediates such as free radicals, carbenes, and carbonyl oxides (also known as Criegee intermediates). , These intermediates are important in atmospheric, plasma, and combustion chemistry; consequently, there is considerable interest in understanding their photochemical production, characterizing their spectra, and studying the mechanisms and kinetics of their reactions.…”