1. Introduction

2. Observations and Analysis  
2.1. Laboratory Spectroscopy Data  
2.2. Abundances

3. Results  
3.1. Excitation Temperature  
3.2. Column Densities and Ratios

4. Discussion  
4.1. Column Densities and Excitation Temperature  
4.2. Deuterium Fractionation  
4.3. Other Isotopic Ratios  
4.4. The Path to More Complex Molecules

5. Summary and Outlook