Communication: State-to-state photoionization and photoelectron study of vanadium methylidyne radical (VCH)

Abstract

By employing the infrared (IR)-ultraviolet (UV) laser excitation scheme, we have obtained rotationally selected and resolved pulsed field ionization-photoelectron (PFI-PE) spectra for vanadium methylidyne cation (VCH+). This study supports that the ground state electronic configuration for VCH+ is …7σ28σ23π49σ1 $(\tilde X$(X̃2Σ+), and is different from that of …7σ28σ23π41δ1 ($\tilde X$X̃2Δ) for the isoelectronic TiO+ and VN+ ions. This observation suggests that the addition of an H atom to vanadium carbide (VC) to form VCH has the effect of stabilizing the 9σ orbital relative to the 1δ orbital. The analysis of the state-to-state IR-UV-PFI-PE spectra has provided precise values for the ionization energy of VCH, IE(VCH) = 54 641.9 ± 0.8 cm−1 (6.7747 ± 0.0001 eV), the rotational constant B+ = 0.462 ± 0.002 cm−1, and the v2+ bending (626 ± 1 cm−1) and v3+ V–CH stretching (852 ± 1 cm−1) vibrational frequencies for VCH+($\tilde X$X̃2Σ+). The IE(VCH) determined here, along with the known IE(V) and IE(VC), allows a direct measure of the change in dissociation energy for the V–CH as well as the VC–H bond upon removal of the 1δ electron of VCH($\tilde X$X̃3Δ1). The formation of VCH+($\tilde X$X̃2Σ+) from VCH($\tilde X$X̃3Δ1) by photoionization is shown to strengthen the VC–H bond by 0.3559 eV, while the strength of the V–CH bond remains nearly unchanged. This measured change of bond dissociation energies reveals that the highest occupied 1δ orbital is nonbonding for the V–CH bond; but has anti-bonding or destabilizing character for the VC–H bond of VCH($\tilde X$X̃3Δ1).

Rotationally resolved state-to-state photoionization and photoelectron study of titanium carbide and its cation (TiC/TiC+)

“…Table II. The previous rotationally resolved state-to-state PFI-PE studies of CH 3 I/CH 3 I + , 27 CH 3 Br/CH 3 Br + , 28 FeC/FeC + , 1 NiC/NiC + , 2 CoC/CoC + , 3 TiO/TiO + , 10 VN/VN + , 11 VCH/VCH + , 4 and NbC/NbC +12 show that rotational photoionization transition depends on | N + | = | N + − J | with the minimum | N + | transition having the maximum intensity. Furthermore, the intensity of rotational transition was found to decrease as | N + | increases.…”

“…The PFI-PE detection scheme used was similar to that of previous studies. [1][2][3][4] In order to minimize the destruction of high-n Rydberg species, the PI/PEX region was kept electric field free during the laser photoexcitation. This was achieved by grounding the upper and lower electron repeller plates, which defined the PI/PEX region.…”

“…The high resolution spectroscopic studies of MX/MX + systems can be viewed a) Electronic mail: cyng@ucdavis.edu as the first step for a detailed understanding of the nature of chemical bonding between transition metal and main group elements. [1][2][3][4][5][6][7] The high-resolution spectroscopic studies of many neutral MX species have been reported previously. 5,8,9 However, due to the difficulty in preparing MX + cations with high intensities, high-resolution spectroscopic studies of these cations by conventional spectroscopic techniques are lacking.…”

“…5,8,9 However, due to the difficulty in preparing MX + cations with high intensities, high-resolution spectroscopic studies of these cations by conventional spectroscopic techniques are lacking. By taking advantage of the existence of low lying multiplicity electronic states in the infrared (IR) and visible (VIS) regions, we have recently succeeded in recording rotationally resolved state-to-state pulsed field ionizationphotoelectron (PFI-PE) spectra for an array of transition metal-containing diatomic and triatomic molecular systems, including FeC/FeC + , 1 NiC/NiC + , 2 CoC/CoC + , 3 TiO/TiO + , 10 VN/VN + , 11 VCH/VCH + , 4 and NbC/NbC +12 by using the two-color infrared-ultraviolet (IR-UV) or visible-ultraviolet (VIS-UV) resonance-enhanced photoexcitation schemes. The present study is an extension of this effort, aiming to examine the molecular structures and bonding properties of the TiC/TiC + system by employing the VIS-UV photoionization efficiency (PIE) and VIS-UV-PFI-PE methods.…”

High-Level Ab Initio Predictions for the Ionization Energy, Bond Dissociation Energies, and Heats of Formation of Vanadium Methylidyne Radical and Its Cation (VCH/VCH+)

“…Recently, we have reported a two-color laser photo-ionization and PFI-PE experiment on VCH . The analysis of the state-to-state PFI-PE spectra has provided precise values for the IE of VCH, IE­(VCH) = 54 641.9 ± 0.8 cm –1 (6.7747 ± 0.0001 eV), the rotational constant B + = 0.462 ± 0.002 cm –1 , and the ω 2 + bending (626 ± 1 cm –1 ) and ω 3 + V–CH stretching (852 ± 1 cm –1 ) vibrational frequencies for VCH + ( X 2 Δ 3/2 ), which has its ground state previously assigned as X 2 Σ + in ref .…”