@Article{JChemPhys_109_9870,
author = {S. Schenker and A. Hauser and W. Wang and I.Y. Chan},
title = {{High-spin -> low-spin relaxation in [Zn$_{1-x}$Fe$_{x}$(6-mepy)$_{3-y}$(py)$_{y}$tren](PF$_{6}$)$_{2}$}},
journal= {J. Chem. Phys.},
ISSN = {0021-9606},
volume= {109},
number= {22},
pages = {9870-9878},
url = {http://jcp.aip.org/jcpsa6/v109/i22/p9870_s1?isAuthorized=no},
eprint= {http://www.unige.ch/sciences/chifi/publis/refs_pdf/ref00180.pdf},
doi= {10.1063/1.477681},
abstract = {{The thermal spin transition in the diluted mixed crystal [Zn$_{1-{\em x}}$Fe$_{{\em x}}$(6-mepy)$_{3}$tren](PF$_{6}$)$_{2}$ ({\em x} = 0.00025, (6-mepy)$_{3}$tren = {\em t}{\em r}{\em i}{\em s}{4-[(6-methyl)-2-pyridyl]-3-aza-3-butenyl}amine) is studied at 1 bar and 1 kbar by temperature-dependent absorption spectroscopy. From thermodynamic analysis of the high-spin (HS) fractions, values for $\Delta${\em H}$_{HL}^0$ and $\Delta${\em S}$_{HL}^0$ of 1551(50) cm$^{-1}$ and 7.5(5) cm$^{-1}$/K and a molecular volume of reaction, $\Delta${\em V}$_{HL}^{0}$, of 22(2) Ã
$^{3}$result. Reconsideration of the cooperative effects in the neat [Fe(6-mepy)$_{3}$tren](PF$_{6}$)$_{2}$from Adler et al. [Hyperfine Interact. 47, 343 (1989)] result in a lattice shift, $\Delta$, of 208(15) cm$^{-1}$ and an interaction constant, $\Gamma$, of 109(15) cm$^{-1}$. Temperature-dependent laser flash photolysis experiments in the spin-crossover system [Zn$_{1-{\em x}}$Fe$_{{\em x}}$(6-mepy)$_{3}$tren](PF$_{6}$)$_{2}$ and the LS system [Zn$_{1-{\em x}}$Fe$_{{\em x}}$(py)$_{3}$tren](PF$_{6}$)$_{2}$ in the pressure range between 1 bar and 1 kbar are presented. Above â100 K the HSâLS (low-spin) relaxations behave classically, whereas they become almost temperature independent below 50 K. At ambient pressure, the low-temperature tunneling rate constant in[Zn$_{1-{\em x}}$Fe$_{{\em x}}$(py)$_{3}$tren](PF$_{6}$)$_{2}$ is more than three orders of magnitude larger than the one in[Zn$_{1-{\em x}}$Fe$_{{\em x}}$(6-mepy)$_{3}$tren](PF$_{6}$)$_{2}$. External pressure of 27 kbar accelerates the low-temperature tunneling process by almost nine orders of magnitude. The kinetic results are discussed within the theory of nonadiabatic multiphonon relaxation.}},
year = {1998}
}