Electronic and infrared spectra of H2C3H+ and cyclic C3H3+ in neon matrices

Abstract

The A 1A′←X 1A1 electronic transition of the propargyl cation H2C3H+ with the origin band at 267.8(2) nm has been identified in a neon matrix at 5 K. The frequencies of the two modes excited in the upper state are 667(50) and 1629(50) cm−1 and imply a reduction of symmetry from C2v in the ground state to Cs in the excited state. The most intense IR mode of the propargyl cation is observed at 2079.9(1.0) cm−1 and for the cyclopropenyl cation at 3130.4(1.0) cm−1. Ab initio calculations on the excited states of the two isomer cations support the assignment and explain why the electronic transition could not be observed for the cyclic species; it lies below 200 nm. The A 2A″←X 2B1 and B 2A′←X 2B1 absorptions of the neutral propargyl radical have also been observed with origin bands at 351.9(2) and 343.0(2) nm, respectively. These results provide the basis for the study of these astrophysically interesting C3H3+ species in the gas phase.

Low‐Temperature Experiments on the Formation of Deuterated C3H+3

“…For preparing C 3 H þ 3 ions, allene CH 2 ¼ C ¼ CH 2 (Aldrich, 97%) has been used as neutral precursor. Also, C 3 H þ 3 exists in two different isomeric forms, the cyclic one being the ground state while the H 2 C 3 H þ structure is 106 kJ mol À1 higher in energy (Wyss et al 2001). It is known from the literature …”

Propargyl Radical: Ab Initio Anharmonic Modes and the Polarized Infrared Absorption Spectra of Matrix-Isolated HCCCH2

“…20 More recent experiments clearly show a pair of closely spaced excited states for the propargyl radical. 22 A weak set of bands was assigned as 0 0°( Ã 2 A′′ r X 2 B 1 ) ) 28 409 cm -1 (3.52 eV) whereas the stronger set of features was identified as the 0 0°( B 2 A′ r X 2 B 1 ) ) 29 146 cm -1 (3.61 eV) transition. A third HCd C-CH 2 band system has recently been observed 23 in the spectral range of 230-300 nm.…”

Matrix isolation study of the interaction of excited neon atoms with allene and propyne: Infrared spectra of H2CCCH2+ and H2CCCH−

“…Several of the vibrational fundamentals of propargylium, selectively prepared from propargyl compounds, were determined from photoelectron and zero electron kinetic energy ͑ZEKE͒ measurements by Minsek and Chen 17 and by Gilbert and co-workers. 18 Very recently, Wyss and co-workers 19 reported the detection of one infrared absorption each for massselected cyc-C 3 H 3 ϩ and propargylium trapped in solid neon, as well as an electronic transition of propargylium.…”