# Rotational excitation of CN by ortho-H2 (Kalugina et al, 2013)

Display rate coefficients as : Display rate coefficients graphically : Data information :
• CN initial level labelled from 2 to 16
• CN final level labelled from 1 to 15
• H2 initial level labelled from 1 to 1
• H2 final level labelled from 1 to 1
• 21 temperatures between 5 K and 300 K
• Units : cm3 s-1

CN

H2

CN

N/A

Reduced Mass = 1.8964 a.m.u.

### References :

None

The calculation of the PES assumes that both CN and H2 are rigid rotors. For H2, the bond distance is fixed to the value averaged over the fundamental vibration mode, i.e. rHH = 1.4487 a0. For CN, the equilibrium distance is taken, i.e. rCN = 2.2144 a0. The reactive channel towards HCN + H is ignored, given that this reaction have an activation energy of at least 1100 cm-1 (Ter Horst et al, 1996).

The CN-H2 PES was calculated at the RCCSD(T) / aug-cc-pVTZ level of theory. The basis was supplemented with mid bond functions. The basis set superposition error (BSSE) was corrected at all geometries with the Boys and Bernardi counterpoise procedure (Boys and Bernardi 1970). The AVTZ + bond functions was found to reproduce higher basis sets calculations (i.e. AV5Z) within ~1-2 cm-1 in the potential well.

The calculations were performed at regularly spaced distances in the range 4-16 a0. At each distance, the angular dependence was sampled on a predefined grid for the 3 angles that describe the 4D PES. The analytical behaviour of the PES was obtained by fitting the ab intio points with the expression reported in Green et al. 1975, and, at every intermolecular distance R, consists in 68 angular terms . The ab initio points at distances larger than 12 a0 were discarded from the fitting procedure, since irregularities characteristic of non-convergence were observed in the long range part of the PES. The radial coefficients were subsequently fitted along the R coordinate, with an exponential dependence below 4.5 a_0 and with polynomials of 1/Rn where n=[2;12] in the range 4.5-12 a0. The errors reported for the fitting procedure are: ~1% in the attractive part of the PES (the minimum being at -121 cm-1) and ~2-3% in the short range repulsive part. The polynomial fit (performed in the range 10-12 a0) is used to extraplate the PES at distances larger than 12 a0. Comparison between extrapolated and available ab initio points shows a reasonnable agreement (not quantified).

### References :

Close-coupling (CC) calculations were performed for total energies ET < 2000 cm-1, and solving the spin-free coupled set of differential equations. The integration was performed between 4.5 and 50 a0. The last ab initio points considered in the fit was at 12 a0 and the radial dependence was extrapolated from the fit of the radial terms.

### References :

None

0 to 2000 cm-1

The number of CN rotational states was adjusted to ensure convergence (1-2%) of the first 16 rotational states (N1 = 15), and typically include 2 closed rotational levels. The j=1 and 3 ortho-H2 rotational states were included at all energies.

The accuracy of the PES was tested from bound states calculations. The theoretical binding energy for the CN-H2 complex was found in perfect agreement with the experimental value of 38 cm-1 (Chen et al, 1998).

The current rate coefficients are expected to be accurate within a few percents according to the current PES.

## Presentation

De-excitation rate coefficients are provided for the first 16 rotational energy levels of CN in collision with ortho-H2, for temperatures in the range 5-300K.

## References

NB : the main reference is displayed in red