Ti₂: Accurate Determination of the Dissociation Energy from Matrix Resonance Raman Spectra and Chemical Interaction With Noble Gases

Abstract

UV-visible and resonance Raman spectra of Ti(2) isolated in Ar, Kr, and Xe matrices at temperatures of 10 K were measured by using the 514 nm line of an Ar ion laser. The data show that the Ti(2) molecule interacts strongly with Xe, leading to a significant weakening of the Ti[bond]Ti bond strength. The f(Ti[bond]Ti) force constant decreases in the series Ar>Kr>Xe, from 232.8 Nm(-1) in Ar and 225.5 Nm(-1) in Kr to 199.7 Nm(-1) in Xe. Additional experiments in an Ar matrix containing 2 % of Xe indicate the formation of a molecule of the formula Ti(2)Xe. Our spectra for Ti(2) in an Ar matrix give evidence for several previously not observed members of the Stokes progression. The sum of experimental data allows for an improved estimation of the dissociation energy on the basis of a LeRoy-Bernstein-Lam analysis. A dissociation energy of 1.18 eV was derived from this analysis. The UV-visible data give evidence of the vibrational levels of an excited state of Ti(2).

Intrinsic Dinitrogen Activation at Bare Metal Atoms

“…Previous experiments had led us to study in depth the Ti 2 dimer by using a combination of experimental results and quantum chemical calculations. [99,100] With resonance Raman spectroscopy, it proved possible to detect a series of overtones of the vibrational fundamental of the dimer (Figure 4), which can be used to estimate a dissociation energy to about 120 kJ mol À1 . [101] Quantum chemical multireference CI calculations argue for a somewhat higher value (about 150 kJ mol À1 ).…”

Cleavage of the N2 Triple Bond by the Ti Dimer: A Route to Molecular Materials for Dinitrogen Activation?

“…[4] Herein, we report the reaction with N 2 , which proceeds in a single step without a significant activation barrier to result in complete cleavage of the strong NN triple bond and the formation of a cyclic TiA C H T U N G T R E N N U N G (m-N) 2 Ti molecule. By contrast, a Ti atom in its electronic ground state does not react with N 2 ; matrix-isolation experiments give no spectroscopic evidence to suggest the formation of even a loosely bound complex.…”

“…On the basis of resonance Raman measurements, [4] the TiÀTi bond energy has been estimated to be approximately 120 kJ mol À1 , although quantum chemical calculations [5] suggest a somewhat higher value of 150 kJ mol À1 . We have also characterized several electronically excited states of this interesting molecule by using absorption spectroscopy and quantum chemical calculations.…”

Spaltung der N2‐Dreifachbindung durch Ti2: ein Weg zu molekularen Materialien für die N2‐Aktivierung?

“…Wir haben uns mit der Charakterisierung von Ti 2 beschäftigt, das sich in Inertgasmatrices stabilisieren lässt. Mithilfe der Resonanz-Raman-Spektroskopie [4] konnten wir die Ti-Ti-Bindungsenergie des matrixisolierten Moleküls zu etwa 120 kJ mol À1 abschätzen. Quantenchemische Rechnungen sprechen allerdings für einen etwas höheren Wert (150 kJ mol À1 ).…”

“…[4] Hier berichten wir über die Reaktion mit N 2 , bei der die N 2 -Dreifachbindung praktisch ohne Aktivierungsbarriere in einem einzigen Schritt vollständig gespalten und ein TiA C H T U N G T R E N N U N G (m-N) 2 Mithilfe quantenchemischer Rechnungen wollten wir mehr Informationen über das Reaktionsprodukt und die Thermodynamik dieser ungewöhnlichen Veränderung erhalten. Im Unterschied zu einer früheren Rechnung [9] erhält man mit der Methode der Multireferenz-Konfigurationswech-A C H T U N G T R E N N U N G selwirkung (MRCI), basierend auf Berechnungen des multikonfigurationalen selbstkonsistenten Feldes (MCSCF) mit einem Basissatz aus natürlichen Atomorbitalen (Ti: [7s6p4d3f2g]; N: [5s4p3d2f]), [10] einen 1 A g -Grundzustand, À1 und damit als endotherm berechnet (BP86/def2-TZVP).…”