Infrared spectroscopy of carbo-ions. VI. C–H stretching vibration of the acetylene ion C2H2+ and isotopic species

Abstract

The infrared spectra of the band of the 2Π–2Π asymmetric hydrogen stretching vibration in the three isotopic acetylene ions C2H2+ (ν3), 13C2H2+ (ν3), and DCCH+ (ν1) have been observed and analyzed. The high resolution infrared spectra were recorded using a difference-frequency laser spectrometer as the tunable coherent infrared source probing an ac glow discharge. Velocity modulation, noise subtraction, and unidirectional multipassing of the infrared beam through the discharge cell provided high sensitivity. C2H2+ was produced in a gas mixture of H2, He, and either CH4 or C2H2, with a total pressure of ≊7 Torr in multiple-inlet–outlet air-, water-, and liquid-nitrogen-cooled discharge tubes; C2H2 freezing precluded its use in liquid-N2-cooled discharges. Complicated by a strong perturbation whose maximum occurred at N′=15 for F1 and N′=14 for F2, the assignment of the spectrum of normal C2H2+ was made possible by (1) fortuitous discharge conditions which provided unambiguous discrimination of C2H2+ lines from among concurrent CH3+ and C2H3+ lines, and (2) fitting the ground state combination differences. Sufficiently high N transitions were observed where Λ doubling was evident. The average bond lengths rz(CH)=1.077 (5) Å and rz(CC)=1.257 (8) Å were calculated from the spectroscopic constants determined from nonlinear least-squares fitting. Vibration–rotation interactions, the Renner–Teller interaction of perturbing states, plasma chemistry, and the relevance of the work in astrophysics are discussed.

Double resonance rotational spectroscopy of CH2D+

“…Thus, excluding this line, our data were used as input to an asymmetric rotor model (Western 2016). Transitions from previous publications (Jagod et al 1992;Amano 2010;Gärtner et al 2013) were not included here as they did not significantly improve the ground state constants. The obtained rotational constants for the ground state of CH 2 D + are summarized in Table 2.…”

“…This process is called laser induced reaction (LIR; Schlemmer et al 1999Schlemmer et al , 2002. For this vibrational excitation, a cw optical parametric oscillator (OPO) was held in resonance (within ±2 × 10 −4 cm −1 ) on selected transitions of the ν 1 or ν 4 bands (Jagod et al 1992;Gärtner et al 2013). With the IR frequency held on resonance, a cw (sub)mm-wave beam was shone simultaneously onto the trapped ion ensemble.…”

“…Those searches and tentative detections used predicted CH 2 D + transition frequencies based on laboratory data available at that time. The first predictions of the rotational transition frequencies were provided by the IR data by Rösslein et al (1991) and Jagod et al (1992), and those were later refined by the high-resolution IR work by Gärtner et al (2010Gärtner et al ( , 2013 and, in particular, by the first four pure rotational lines measured by Amano (2010). More recently, two fundamental rotational transitions were measured in the Cologne laboratories (Brünken et al 2014b) using a helium attachment technique at 4 K (Brünken et al 2014a).…”

DETECTION OF NONPOLAR IONS IN2Π3/2STATES BY RADIOASTRONOMY VIA MAGNETIC DIPOLE TRANSITIONS

“…The electronic matrix element for the magnetic dipole operator in these cases is given by (Λ + g e Σ) × 0.009274 D. Thus, these transitions will be weak but potentially observable. (Jagod et al 1992;Kuhn et al 1986). A blackbody radiation temperature of 2.76 K has also been assumed in the calculation.…”

“…Notes. a Spectroscopic constants for H-C≡C-H + from Jagod et al (1992); estimated 1σ errors in line positions, based on the reported 1σ error in B 0 , are 3-12 MHz for the transitions listed, increasing as one moves to higher frequency transitions. b Spectroscopic constants for H-C≡C-C≡C-H + from Kuhn et al (1986); estimated 1σ errors in line positions are 5-50 MHz for the transitions listed.…”