Directed Gas‐Phase Synthesis of Triafulvene under Single‐Collision Conditions

Abstract

The triafulvene molecule (c‐C4H4)—the simplest representative of the fulvene family—has been synthesized for the first time in the gas phase through the reaction of the methylidyne radical (CH) with methylacetylene (CH3CCH) and allene (H2CCCH2) under single‐collision conditions. The experimental and computational data suggest triafulvene is formed by the barrierless cycloaddition of the methylidyne radical to the π‐electron density of either C3H4 isomer followed by unimolecular decomposition through elimination of atomic hydrogen from the CH3 or CH2 groups of the reactants. The dipole moment of triafulvene of 1.90 D suggests that this molecule could represent a critical tracer of microwave‐inactive allene in cold molecular clouds, thus defining constraints on the largely elusive hydrocarbon chemistry in low‐temperature interstellar environments, such as that of the Taurus Molecular Cloud 1 (TMC‐1).

Low-temperature gas-phase formation of indene in the interstellar medium

“…The reaction of the methylidyne (CH; X 2 Π) radical with styrene (C 8 H 8 ; X 1 A′) was performed in gas phase under single collision conditions exploiting a crossed molecular beam machine ( 67 ). A pulsed supersonic beam of methylidyne radicals was produced by photodissociation of helium (99.9999%; Air Gas)–seeded bromoform (CHBr 3 , ≥ 99%; Aldrich Chemistry) held in a stainless steel bubbler at a stagnation pressure of 2.2 atm and 283 K. This mixture was introduced into a pulsed piezoelectric valve operating at a repetition rate of 60 Hz, pulse widths of 80 μs, and a peak voltage of −400 V. The 248-nm output of excimer laser (30 Hz; COMPex 110, Coherent Inc.) intersected molecular beam 1 mm downstream of the nozzle ( 68 ). A chopper wheel rotating at 120 Hz selected a section of the pulse defined by a peak velocity of 1850 ± 11 ms −1 and speed ratio of 11.7 ± 0.7.…”

Gas-Phase Formation of 1-Methylcyclopropene and 3-Methylcyclopropene via the Reaction of the Methylidyne Radical (CH; X2Π) with Propylene (CH3CHCH2; X1A′)

“…These findings suggest further that the hydrogen atom loss to p2 and p3 operates on a time scale that is faster than any isomerization of i1/i2 formed via methylidyne addition. Compared to related reactions of methylidyne with methylacetylene/allene, 67,82 the barrierless cycloaddition of the methylidyne radical to the carbon−carbon triple/double bond of methylacetylene/allene also reveals a non-RRKM behavior leading via atomic hydrogen emission to the triafulvene product in both systems with atomic hydrogen being emitted from the methyl group of the methylacetylene reactant and from the CH 2 moiety of allene, respectively. Note that previously, two kinetic experiments were performed on the methylidyne−propylene system.…”

Gas-Phase Formation of C5H6 Isomers via the Crossed Molecular Beam Reaction of the Methylidyne Radical (CH; X2Π) with 1,2-Butadiene (CH3CHCCH2; X1A′)

“…The methylidyne (CH; X 2 Π) radical reaction with 1,2-butadiene (CH 2 CCHCH 3 ; X 1 A′) was conducted under single collision conditions using a crossed molecular beams machine at the University of Hawaii . In the primary source chamber, the pulsed methylidyne molecular beam was formed via photodissociation (COMPex 110, Coherent, Inc.; 248 nm; 30 Hz) of bromoform (CHBr 3 , Aldrich Chemistry, ≥99%) seeded in helium (99.9999%; AirGas) at fractions of 0.12% at a backing pressure of 2.2 atm. , The methylidyne beam passed a skimmer and was velocity selected by a four-slot chopper wheel yielding a peak velocity v p of 1827 ± 15 m s –1 and speed ratio S of 12.0 ± 1.2. The rotational temperature of the methylidyne radicals were determined to be 14 ± 1 K via laser-induced fluorescence (LIF) .…”