How to serialize this XML?

The bit you're missing is the IXmlSerializable interface. Because your XML is not a standard XML produced by the .Net serialization libraries. You'll require a custom process.

IXmlSerializable Interface[^]

public class Recognition : IXmlSerializable
{

  public string radio;
  public DateTime date;
  public string file;
  public string listenTime;
  public string intervalTime;

  public XmlSchema GetSchema() { return null; }

  public void WriteXml (XmlWriter write) 
  { 
    //write to xml here
  }

  public void ReadXml (XmlReader reader)
  {
    radio = XmlReader.Attributes["radio"];
    //handle other attributes here
  }

}