Mass-Resolved Nanosecond Laser Spectroscopy of Jet-Cooled Ferrocene in the Region of the 3d_z² → R4p_x,y One-Photon Rydberg Transition

Abstract

The wavelength-dependent mass-selected ion signals produced by supersonic-cooled ferrocene irradiated with nanosecond laser pulses in the region of the 3d z 2 f R4p x,y transition (40 000-42 000 cm -1 ) have been investigated. Surprisingly, in a one-color multiphoton experiment, conditions have been found for the formation of intact molecular ions (C 5 H 5 ) 2 Fe + as the only ionic product. Neutral iron atoms are generated, however, in large amounts under these conditions by the photodissociation of the ferrocene molecules. Multiphoton ionization of the Fe atoms by the second UV laser makes it possible to reveal a resolved vibronic structure of the ferrocene Rydberg transition. The two-color multiphoton dissociation/multiphoton ionization spectrum shows a 0 0 0 peak at 41 090 cm -1 and a 4 0 1 component at 41 410 cm -1 demonstrating better resolution than the one-photon absorption spectrum measured in a static cell at elevated temperature. The distance between the vibronic components corresponds to the symmetric metal-ligand stretch in the Rydberg state. The twocolor mass spectrum is changed dramatically when the second laser operates in the 17 500-cm -1 region. In this case, the excited states populated by the first laser are ionized efficiently by the second one, and the intensity of the molecular ion signal increases significantly. The REMPI excitation spectra measured at the masses of (C 5 H 5 ) 2 Fe + and fragment ions agree very well with that derived from the ionization of neutral iron atoms and reveal the same vibronic structure of the 3d z 2 f R4p x,y transition in the ferrocene molecule.

High-Resolution Mass-Analyzed Threshold Ionization Study of Deuterated Derivatives of Bis(η6-benzene)chromium

“…Only for chromocene has a low-resolution molecular REMPI spectrum containing one broad structureless band been obtained. 24 On the other hand, recently we have demonstrated that ferrocene, 25,26 nickelocene, 27 and 1 28 can be efficiently ionized with nanosecond laser pulses when the transition from the metallocalized 3d z 2 orbital to the lowest Rydberg p x,y level is used as the first step of the multiphoton excitation. The REMPI spectrum of 1 28 revealed a structured Rydberg transition with wellresolved vibronic components.…”

Dissociation Dynamics and Electronic Structures of Highly Excited Ferrocenium Ions Studied by Femtosecond XUV Absorption Spectroscopy

“…Finally, we can compare the effects of NIR SFI to photolysis using UV lasers. Using nanosecond lasers, fragmentation has been observed with wavelengths ranging from the visible to the deep UV. − A key distinction is that these experiments have sufficiently long laser pulses to ionize or further fragment any products of the initial dissociation. The general mechanism to give either single or double ring loss was found to be one of photon cycling, i.e., repeated absorption of a photon followed by internal conversion, until enough energy has been deposited to break a bond.…”

Probing of an Adsorbate-Specific Excited State on an Organic Insulating Surface by Two-Photon Photoemission Spectroscopy

“…In free molecules in the gas phase, excited states bound to ionic cores have been observed as Rydberg states. [24][25][26]28,29 The gas-phase UV absorption spectrum of Fc clearly reveals that electronic transition from the nonbonding iron 3d (a 1g ) orbital to the molecular Rydberg 4p (e 1u ) orbital occurs at an excitation energy of 5.1 eV. [24][25][26]28,29 In our study of Fc molecules adsorbed on the SAM, excitation from H1 to A* at 4.57 ((4.54−4.59)/2) eV, shown in Figure 3, seems to correspond to excitation from 3d to Rydberg 4p (5.1 eV in free Fc molecules), where the excitation energy is lowered by induced image charges in the substrate.…”

“…[24][25][26]28,29 The gas-phase UV absorption spectrum of Fc clearly reveals that electronic transition from the nonbonding iron 3d (a 1g ) orbital to the molecular Rydberg 4p (e 1u ) orbital occurs at an excitation energy of 5.1 eV. [24][25][26]28,29 In our study of Fc molecules adsorbed on the SAM, excitation from H1 to A* at 4.57 ((4.54−4.59)/2) eV, shown in Figure 3, seems to correspond to excitation from 3d to Rydberg 4p (5.1 eV in free Fc molecules), where the excitation energy is lowered by induced image charges in the substrate. According to the above scenario, it can be considered that the potential for electrons in the adsorbate-specific excited state is composed of two contributions including image potential and attraction by the positive hole.…”

“…Fc is a model compound for investigating organometallic systems owing to its high molecular symmetry and its stable closed “18-electron” shell configuration . The physical and chemical properties of Fc have been extensively studied by optical spectroscopy including laser spectroscopy in gas and solution phases − and photoelectron spectroscopy in the gas phase , and adsorbed systems. , Here, we have investigated electronic structures including excited metastable states of Fc adsorbed on the SAM by two-photon photoemission (2PPE) spectroscopy and ultraviolet photoelectron spectroscopy (UPS). 2PPE is a powerful experimental tool for probing electronic structures below and above Fermi level ( E F ) and transient excited states at the surface. , In 2PPE, an electron in an occupied state is excited into an unoccupied state by a first photon, where it is probed by a second photon.…”