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1 Introduction
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2 Observations and data reduction
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3 Ortho/para ratios and their relationship to v= 1-0 S(0) and
S(1) line brightness
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4 Observational constraints on models
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5 PDR as a possible source of excitation
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6 Shocks as a source of H
excitation
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7 Comparison of observations with shock models
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8 Concluding remarks
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References
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Online Material
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Appendix A: Model results for classes A1, A2, B and C and objects 1, 2
and 3
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