Mass spectrometric determination of the dissociation energy of technetium carbide(g)

Abstract

The TcC(g) molecule is observed above a liquid technetium carbide phase of unknown composition by using Knudsen effusion mass spectrometry. Intensity data for Tc(g) between 2229 and 2560 K and for TcC(g) between 2393 and 2595 K give a third-law bond energy of D°0 = (134 ± 7) kcal moT1 for TcC(g). A value of D°0 = (140 ± 2) kcal moT1 is obtained by the second-law method.

Density Functional Investigation of Various States of the Molecules TcC, TcC2, ScC2, and YC2

“…Diatomic 98 TcC is the only carbide molecule of technetium for which a molecular property has been experimentally measured. 4 For this reason, we have chosen to investigate some of the diatomic spin states, in order to assess the performance of the density functional implementation. Diatomic binding energies can also be used to evaluate 98 TcC 2 carbon atom extraction enthalpies.…”

“…The dissociation energy of TcC has been determined experimentally, using electron ionization-Knudsen effusion mass spectrometry, to be 6.02 ( 0.1 eV. 4 Numerous approximations were used in the evaluation of the experimental dissociation energy, including the estimation of (H°2 450 -H°0) ) 0.89 eV, the Gibbs free energy functions for C (s) ,Tc (g) and the estimation of appearance energies for Tc + and TcC + ((0.2 eV, (0.5 eV, respectively). Furthermore, the "equilibrium" assumption does not take into account fragmentations of higher carbides that lead to the formation of TcC.…”

“…On a molecular scale, the diatomic TcC has been detected in the vapor above a technetium-graphite melt. 4 Our interest in the simple carbide molecules TcC and TcC 2 stems from spectroscopic investigations 5,6 of the 99m Tc-labeled microaerosols Technegas 7 and Pertechnegas 8 used in the diagnosis of pulmonary disorders. The "99 m" is reference to the metastable isotope of technetium (τ 1/2 ) 6.02 h, γ ) 140 keV, internal conversion) 9 that is widely used in single-photon emission computed tomography.…”

“…Furthermore, TcC x ≥ 2 molecules may be important precursors for the growth of such phases. On a molecular scale, the diatomic TcC has been detected in the vapor above a technetium−graphite melt …”

Phase transition, elastic and thermodynamical properties of TcC under high pressure from first-principles calculations

“…Recently, it was reported that the development of potential Tc-rich nitride forms with high chemical stability and corrosion resistance [7]. In addition, Tc carbides appear to have especially surprising importance in the fields of nuclear waste management and nuclear medicine [8,9]. Therefore, there is great interest for physicists in experimental [8][9][10][11][12] and theoretical investigations [13,14,25] of technetium carbides.…”