The ultraviolet spectrum of the CoCl2 radical, studied at vibrational and rotational resolution

Abstract

The laser excitation spectrum of the 327 nm band system of CoCl2, formed in a free-jet expansion, has been recorded at a rotational temperature of approximately 10 K. The spectrum is congested and suffers extensive perturbations. A progression in the excited state symmetric stretching vibration has been identified. The decrease in the symmetric stretching vibrational wave number on excitation is considerable [nu1 '=195.7(12), nu1 (")=358.1(17) cm(-1)]. Despite widespread perturbations in the rotational structure of these vibronic bands, they can be confidently assigned to a parallel Omega=72-72 transition, consistent with an inverted 4Deltag ground electronic state. The rotational constant for Co35Cl2 in the ground state is determined to be 0.056 65(11) cm(-1), which corresponds to a value for the zero-point averaged Co-Cl bond length r0 of 2.062 8(40) A. The perturbations are found to be strongly isotopomer dependent.

Rotational and vibrational structure in the 288nm band system of the FeCl2 radical

“…It will be shown that the previous assignment was incorrect; these transitions involve the symmetric stretching vibration that is greatly reduced from its ground state value of 352 to 200 cm À1 in the excited state. Similar behavior is observed in the 327 nm band system of CoCl 2 [6]. All the bands are degraded to the red and have easily distinguishable R-branch heads.…”

“…The excited state potential is also found to be significantly more anharmonic than that of the ground state ðx 0 0 11 ¼ À2:525ð47Þ cm À1 ; x 0 00 11 ¼ À0:946ð12Þ cm À1 Þ. In both respects, the behavior observed in this band system of FeCl 2 mirrors that of the 327 nm band system of CoCl 2 [6].…”

“…Those studied so far include FeCl 2 [4,5], CoCl 2 [6], NiCl 2 [7], and CuCl 2 [8]. Our preliminary observations of the 288 nm system of FeCl 2 were reported in a recent communication [4].…”

“…The identification of FeCl 2 as the carrier of the spectrum is based on arguments presented in a previous publication [4]. To these we can add that the ground state vibrational interval of 352.39(13) cm À1 determined by dispersing the laser-induced fluorescence from several vibronic bands in this system [5] is entirely consistent with that expected by analogy with CoCl 2 [6], NiCl 2 [2] and CuCl 2 [31]. The ground state rotational parameter, B 00 0 , for Fe 35 Cl 2 is determined to be 0.0530296(95) cm À1 , which is also consistent with a linear first-row transition metal dichloride.…”

“…The best signal-to-noise was obtained at a stagnation pressure of 1.5 atm, and the signal strength decreased markedly as the stagnation pressure was raised, to the extent that, by 4 atm, the signal was barely above the level of the noise. The analogous reaction between cobalt wire and HCl shows a very similar pressure dependence [6]. However, this effect was not observed with nickel and HCl.…”