# rmgpy.pdep.SingleExponentialDown¶

class rmgpy.pdep.SingleExponentialDown(alpha0=None, T0=None, n=0.0)

A representation of a single exponential down model of collisional energy transfer. The attributes are:

Attribute Description
alpha0 The average energy transferred in a deactivating collision at the reference temperature
T0 The reference temperature
n The temperature exponent

Based around the collisional energy transfer probability function

$P(E, E^\prime) = C(E^\prime) \exp \left( -\frac{E^\prime - E}{\alpha} \right) \hspace{40pt} E < E^\prime$

where the parameter $$\alpha = \left< \Delta E_\mathrm{d} \right>$$ represents the average energy transferred in a deactivating collision. This is the most commonly-used collision model, simply because it only has one parameter to determine. The parameter $$\alpha$$ is specified using the equation

$\alpha = \alpha_0 \left( \frac{T}{T_0} \right)^n$

where $$\alpha_0$$ is the value of $$\alpha$$ at temperature $$T_0$$ in K. Set the exponent $$n$$ to zero to obtain a temperature-independent value for $$\alpha$$.

T0

The reference temperature.

alpha0

The average energy transferred in a deactivating collision at the reference temperature.

calculateCollisionEfficiency(self, double T, ndarray Elist, ndarray Jlist, ndarray densStates, double E0, double Ereac)

Calculate an efficiency factor for collisions, particularly useful for the modified strong collision method. The collisions involve the given species with density of states densStates corresponding to energies Elist in J/mol, ground-state energy E0 in kJ/mol, and first reactive energy Ereac in kJ/mol. The collisions occur at temperature T in K and are described by the average energy transferred in a deactivating collision dEdown in kJ/mol. The algorithm here is implemented as described by Chang, Bozzelli, and Dean [Chang2000].

 [Chang2000] A. Y. Chang, J. W. Bozzelli, and A. M. Dean. Z. Phys. Chem. 214, p. 1533-1568 (2000). doi: 10.1524/zpch.2000.214.11.1533
generateCollisionMatrix(self, double T, ndarray densStates, ndarray Elist, ndarray Jlist=None)

Generate and return the collision matrix $$\matrix{M}_\mathrm{coll} / \omega = \matrix{P} - \matrix{I}$$ corresponding to this collision model for a given set of energies Elist in J/mol, temperature T in K, and isomer density of states densStates.

getAlpha(self, double T) → double

Return the value of the $$\alpha$$ parameter - the average energy transferred in a deactivating collision - in J/mol at temperature T in K.

n`

n – ‘double’