Rovibronically Selected and Resolved Two-Color Laser Photoionization and Photoelectron Study of the Iron Carbide Cation

Abstract

By using a two-color laser excitation-photoionization scheme, we have obtained rovibronically selected and resolved state-to-state pulsed field ionization-photoelectron (PFI-PE) bands for FeC+(X2delta5/2; v+=0-2, J+), allowing unambiguous rotational assignments for the photoionization transitions. The finding of the J+ = 5/2 level as the lowest rotational state confirms that the ground FeC+ ion state is of 2delta5/2 symmetry. The observed changes in total angular momentum upon photoionization of FeC are |deltaJ+| = |J+ - J'| </= 3.5, indicating that the photoelectron orbital angular momentum is limited to l </= 3. This observation is also consistent with the conclusion that the photoionization involves the removal of an electron from the highest occupied molecular orbital of the pi-type. The ionization energy, IE = 61243.1 +/- 0.5 cm(-1) (7.59318 +/- 0.00006 eV), for the formation of FeC+ (X2delta5/2, v+=0; J+=5/2) from FeC (X3delta3, v"=0; J"=3), the rotational constants, Be+ = 0.7015 +/- 0.0006 cm(-1) and alphae+ = 0.00665 +/- 0.00036 cm(-1), and the vibrational constants, omegae+ = 927.14 +/- 0.04 cm(-1) and omegae+chie+ = 6.35 +/- 0.04 cm(-1), for FeC+(X2delta5/2) determined in the present study are compared to the recent state-of-the-art ab initio quantum chemical calculation at the C-MRCI+Q level of theory. The large deviation (0.49 eV) observed between the present experimental IE value and the C-MRCI+Q theoretical IE prediction highlights the great need for the further development of ab initio quantum theoretical procedures for more accurate energetic predictions of transition metal-containing molecules.

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

“…This observed D 0 change reveals the highest occupied 1δ orbital is nonbonding in nature for the V-CH bond; but has anti-bonding or destabilizing character for the VC-H bond of VCH(X 3 By parking the IR ω 1 at the R-branch band head of the VCH*( + spectra (bottom spectra), which are shown as the orange, purple, brown, green, and red spectra, respectively. The simulation [12][13][14][15] assumes a Gaussian instrumental profile (FWHM = 1.3 cm −1 ) for the PFI-PE detection and takes into account the bandwidth of ω 1 , the Boltzmann populations of J -rotational levels based on an estimated rotational temperature of 35 K for the VCH molecular beam, and the overlaps of the rotational transitions with the excitation profile of the ω 1 output. The N + -dependence of the photoionization cross sections follows the patterns observed in the present and previous single J -selected PFI-PE measurements.…”

“…We have recently succeeded in performing high-resolution pulsed field ionizationphotoelectron (PFI-PE) 9, 10 studies for diatomic MX + (X = C, O, and N) species based on two-color visibleultraviolet (VIS-UV) excitation scheme, which has allowed fully rotationally selected and resolved spectroscopic measurement for MX + cations. [11][12][13][14][15][16] These studies have not only provided reliable rovibrational constants, but also accurate ionization energies (IEs) of MXs. To our knowledge, a fully rotationally resolved PFI-PE measurement for triatomic transition metal-containing cations has not been reported previously.…”

“…19 The experimental apparatus and procedures used are similar to those reported previously. [12][13][14][15] Cold VCH molecules in the form of a pulsed supersonic beam (30 Hz) were prepared by using a laser ablation beam source. 20 The VCH molecules were produced in the ablation source by reactions between laser ablated V species and CH 4 .…”

Communication: A vibrational study of titanium dioxide cation using the vacuum ultraviolet laser pulsed field ionization-photoelectron method

“…4,5 In an effort to improve the precision of the energetic database for simple transition metal oxides and carbides, we have initiated a research program to perform high-resolution PIE and PFI-PE measurements of transition metal-containing species. 6 The IEs of many of the transition metal carbides and oxides are in the vacuum ultraviolet (VUV) range of 6.5-10.0 eV. When a stable intermediate neutral state for these species is known, they are ideal candidates for two-color visible-ultraviolet laser PIE and PFI-PE studies, 6 from which highly precise IE and spectroscopic values can be determined by rotationally selected and resolved photoelectron measurements.…”

Millimeter-wave spectroscopy of CrC (X3Σ−) and CrCCH (X̃ 6Σ+): Examining the chromium-carbon bond

“…8 In the case of the diatomic carbides, optical spectroscopy has been carried out for FeC, CoC, NiC, VC, and, more recently, TiC. [10][11][12][13][14] Pure rotational data have been recorded for FeC, CoC, and NiC as well. 15,16 These studies have demonstrated that the ground states of these molecules are 3 ∆, 2 Σ + , 1 Σ + , 2 ∆, and 3 Σ + , respectively.…”