Perturbation facilitated double-resonant four-wave mixing is applied to access high-lying vibrational levels of the X 1Σg+ (0g+) ground state of Cu2. Rotationally resolved transitions up to v″ = 102 are measured. The highest observed level is at 98% of the dissociation energy. The range and accuracy of previous measurements are significantly extended. By applying the near dissociation equation developed by Le Roy [R. J. Le Roy, J. Quant. Spectrosc. Radiat. Transfer 186, 197 (2017)], a dissociation energy of De = 16 270(7) hc cm−1 is determined, and an accurate potential energy function for the X 1Σg+ (0g+) ground state is obtained. Molecular constants are determined from the measured transitions and by solving the radial Schrödinger equation using this function and are compared with results from earlier measurements. In addition, benchmark multi-reference configuration interaction computations are performed using the Douglas–Kroll–Hess Hamiltonian and the appropriate basis of augmented valence quadruple ζ type. Coupled-cluster single, double, and perturbative triple calculations were performed for comparison.
The first observation of an excited 0 + g state of dicopper is reported. "g" inversion symmetry states are not observable by direct one-photon absorption from the X 1 Σ + g ground state. Measurements are performed by applying nonlinear two-color resonant four-wave mixing (TC-RFWM) spectroscopy. Cold Cu 2 molecules in a molecular beam environment are generated by applying a pulsed laser vaporization source and subsequent near supersonic expansion of the vaporized metal plume entrained in a helium pulse. Spectra in the wavenumber region of the [37.5(v)]0 + g-B0 + u electronic transition are recorded by using the UNFOLDED double-resonance scheme. Specific rotational levels of the intermediate state B0 + u , v ′ = 1 are accessed from the X 1 Σ + g ground state. Dipole selection rules from the labeled levels define unambiguously the rotational quantum number and symmetry of the final state (ΔJ = ±0, 1 and g ↔ u). The UNFOLDED scheme is verified by additional measurements via the origin level, v ′ = 0, of the intermediate B0 + u state. Spectroscopic constants of the [37.5(v)]0 + g state have been determined for both 63 Cu 2 and 63 Cu 65 Cu isotopologues by analysis of the rotationally resolved spectra. The potential of TC-RFWM to study the unexplored "g" symmetry manifold of Cu 2 is discussed.
A highly excited electronic state of dicopper is observed and characterized for the first time. The [39.6] 0u+ -X 1Σg+(0g+) system is measured at rotational resolution by using degenerate and two-color resonant four-wave-mixing, as well as laser induced fluorescence spectroscopy. Double-resonance experiments are performed by labeling selected rotational levels of the ground state by tuning the probe laser wavelength to transitions in the well known (1-0) band of the B 0u+-X 1Σg+(0g+) electronic system. Spectra obtained by scans of the pump laser in the UV wavelength range were then assigned unambiguously by the stringent double-resonance selection rules. The absence of a Q-band suggests a parallel transition (∆Ω = 0) and determines the term symbol of the state as 0u+ in Hund's case (c) notation. The equilibrium constants for 63Cu2 are Te = 39559.921(92) cm−1 , ωe = 277.70(14) cm−1 , Be = 0.104942(66) cm−1 and re = 2.2595(11) Å. These findings are supported by high level ab initio calculations at the MRCI+Q level, which clearly identifies this state as resulting from a 4p ← 3d transition. Additionally, three dark perturber states are found in the v = 1 and v = 2 vibrational levels of the new state. A deperturbation analysis characterizes the interaction and rationalizes the anomalous dips in the excitation spectrum of the [39.6] 0u+ -X 1Σg+ (0g+) system.
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