I don't think you can do what you want with the very "static" XmlSerializer. Here are a couple of helpers that you could get you started with a dictionary (generic or not):

    public static string Serialize(IDictionary dictionary)
    {
        using (StringWriter writer = new StringWriter())
        {
            Serialize(writer, dictionary);
            return writer.ToString();
        }
    }

    public static void Serialize(TextWriter writer, IDictionary dictionary)
    {
        if (writer == null)
            throw new ArgumentNullException("writer");

        using (XmlTextWriter xwriter = new XmlTextWriter(writer))
        {
            Serialize(xwriter, dictionary);
        }
    }

    public static void Serialize(XmlWriter writer, IDictionary dictionary)
    {
        if (writer == null)
            throw new ArgumentNullException("writer");

        if (dictionary == null)
            throw new ArgumentNullException("dictionary");

        foreach (DictionaryEntry entry in dictionary)
        {
            writer.WriteStartElement(string.Format("{0}", entry.Key));
            writer.WriteValue(entry.Value);
            writer.WriteEndElement();
        }
    }

With these helpers, the following code:

        Dictionary<string, string> Identifiers = new Dictionary<string,string>
        {
            { "somename", "somedescription"},
            { "anothername", "anotherdescription" }
        };
        Console.WriteLine(Serialize(Identifiers));

will output this:

<somename>somedescription</somename><anothername>anotherdescription</anothername>

You can adapt to your will.