How to initialise ReadOnlyDictionary?

I have an unchanging dictionary that is exposed in a class.

Currently my code looks like

using System.Collections.Generic;
using System.Collections.ObjectModel;

public class FooClass
{
    private static ReadOnlyDictionary<string, byte> _validRevisions 
        = new ReadOnlyDictionary<string, byte>(
            new Dictionary<string, byte>() { 
                { "1.0", 0x00 },
                { "1.1", 0x01 },
                { "1.2", 0x02 },
                { "1.3", 0x03 }
            } );

    public static ReadOnlyDictionary<string, byte> ValidRevisions => _validRevisions;

    // other FooClass contents...
}

I've used the backing field _validRevisions as I could not figure out a better way of creating a shared constant dictionary property. Is there neater way to manage this or maybe I should just make the field public?

My main question being is there a shorter way to initialise the _validRevisions field itself? Creating a Dictionary inline to pass it into a Dictionary (that happens to be read only) seems a bit... of a code smell. Is it? Is there a better way?

EDIT: one more thing about the ROD I just noticed, there are no methods to support checking if it contains a given value... is there a reason for that related to it' read-only-ness?