1. Aikawa, Y., Herbst, E., ApJ, 351, 233 (1999)
2. Allamandola, L.J., Tielens, A.G.G.M., Barker, J.R., in Interstellar Processes, eds. D.J. Hollenbach & H.A. Thronson, Jr., Dordrecht: D. Reidel, p. 471 (1987)
3. Bauer, I., Finocchi, F., Duschl, W., Gail, H.-P., Schlöder, J., A&A, 317, 273 (1997)
4. Bettens, R.P.A., Herbst, E., ApJ, 468, 686 (1996)
5. Bettens, R.P.A., Herbst, E., ApJ, 478, 585 (1997)