# 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.

as_dict(self) dict

A helper function for dumping objects as dictionaries for YAML files

Returns:

A dictionary representation of the object

Return type:

dict

calculate_collision_efficiency(self, double T, ndarray e_list, ndarray j_list, ndarray dens_states, double E0, double e_reac)

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

generate_collision_matrix(self, double T, ndarray dens_states, ndarray e_list, ndarray j_list=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 e_list in J/mol, temperature T in K, and isomer density of states dens_states.

get_alpha(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.

make_object(self, dict data, dict class_dict)

A helper function for constructing objects from a dictionary (used when loading YAML files)

Parameters:
• data (dict) – The dictionary representation of the object

• class_dict (dict) – A mapping of class names to the classes themselves

Returns:

None

n

‘double’

Type:

n