1. Introduction

2. Observations and Data Reduction

3. Analysis of the Data

3.1. Contribution of the Starburst Ring

3.2. LTE Analysis

4. Results

4.1. Detected and Undetected Molecules

4.2. Rotational Temperatures

4.3. Isotopic Line Ratios

5. Modelling of the Data

5.1. Origin of the Molecules

5.2. Influence of UV Fields and Cosmic Rays on Molecules

5.3. Comparison with the Observations

6. Comparison with Other Galactic Circum Nuclei Regions

6.1. Isotopic Ratios

6.2. Molecular Abundances

7. Conclusions