Infrared laser and Fourier transform spectroscopy of CCH: A highly excited bending vibration of the X̃2Σ+

The 1.66 $μ$m Spectrum of the Ethynyl Radical, CCH

“…This corresponds to shift of the same size, but opposite sign in the T 0 value for the lower level, i.e. T 0 ((020) 2 Σ + ) = 794.251 (12) from the present data, compared to that determined by Chiang et al [19] quoted in table 1 of 794.300 (6).…”

“…These will be good for computing energy levels up to at least J = 23/2, the highest rotational level included in the combination differences data, but likely higher as the present spectral assignments extend to J = 37/2. The hyperfine parameters derived from microwave data [21] in the combined fit, were unchanged from those determined by Le et al [14] With the lower state energies known and fixed, the new data were fit to the upper state energy levels using a Matlab script that set up the 2 Π Hamiltonian operator in the N 2 representation in a parity conserving, case (a) basis set, [12,22] as given in equation (1).…”

“…While the computational results led to an understanding of the vibronic energy levels of the radical, the rotational, fine and even hyperfine structure associated with them has subsequently been an active area of study. The interest lies not only in mapping the complexity and providing spectroscopic avenues for monitoring the radical concentration in, for example, the chemistry of C 2 H with hydrocarbon molecules, [5] in soot formation [6,7,8,9] and in the production of carbon nanotubes, [10] but also in characterizing state couplings [1,11,12] and the kinetics of vibronic relaxation. [13] Herein, we report new high resolution spectra of the radical in a previously unexplored region of the near-infrared in the gas phase.…”

Effect of Noncovalent Interactions on Vibronic Transitions: An Experimental and Theoretical Study of the C2H⋅⋅⋅CO2 Complex

“…[27] It follows that the infrared absorption spectrum of C 2 Hc an be treated quantitatively only by employing av ariationala pproacha nd considering explicitly the three-state vibronic coupling. [28] In this way, Ta rroni and Carter calculated the vibronic transitions [15] and the absorption intensities [29] of C 2 H. The high accuracy of those calculations has been confirmed by the recent experiments on C 2 Hi nt he gas phase, [30,31] with differences of less than 10 cm À1…”

The near-infrared spectrum of ethynyl radical

“…Additional bands of C 2 H in the 4250−4550 cm −1 region have very recently been analyzed in a Fourier transform emission spectrum, and a band near 6340 cm −1 has been characterized by diode laser spectroscopy in a concentration modulated discharge source. 52 Both the calculations 44 and matrix spectrum 45 show that the most intense bands in the entire infrared and near-infrared spectra of the radical lie around 7100 cm −1 or 1.4 µm. The vibronic levels at this energy are strongly mixed, but derive much of their intensity from the near-vertical transition to the A (0,0,2) state, in a region of spectrum where no gas phase spectra have yet been reported.…”