Index was out of range. Must be non-negative and less than the size of the collection. Error when adding objects to a list. C# Unity

Question

I made a class particle in C# and am trying to call the constructor to create another object from that class inside the list lstParticles. I'm not sure why I can't add an object to the list even if the list currently has no items.

The whole error was:

ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index System.Collections.Generic.List`1[T].set_Item (System.Int32 index, T value) (at <88e4733ac7bc4ae1b496735e6b83bbd3>:0) Particles+particle..ctor (System.Single x, System.Single y) (at Assets/Particles.cs:23) Particles.Update () (at Assets/Particles.cs:45)

Here's the code:

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;


public class Particles : MonoBehaviour
{
    public GameObject ParticleWater;
    bool Spawn = false;
    public List<particle> lstParticles = new List<particle> { };
    


    //Class defining particle
    public class particle {
        public List<float> pos = new List<float>();
        public List<float> posLast = new List<float>();
        public List<float> posNext = new List<float>();

        public particle(float x, float y)
        {
            pos[0] = x;
            pos[1] = y;
        }

    }

    

    // Update is called once per frame
    void Update()
    {

        if (Input.GetKeyDown(KeyCode.Space) && Spawn == false)
        {
            Spawn = true;
        } else if(Input.GetKeyDown(KeyCode.Space) && Spawn == true)
        {
            Spawn = false;
        }
        if (Spawn)
        {

            lstParticles.Add(new particle(0, 0));
            //Debug.Log(particle[0]);
        }
        
    }
}

I tried adding an integer to the list with

lstParticles.Add(int 8);
//I also tried:
lstParticles.Add(8);

And got the same error.

Any suggestions on what I am doing wrong?

Edit: So Bing AI helped me figure this one out. I thought the list was occuring because of an error with lstParticles.Add(new particle(0, 0)); but it was actually with the constructor. In the constructer I put

pos[0] = x; pos[1] = y;

So it was trying to set the value of an index that didnt exist.

Bing AI suggested replacing it with

pos.Add(x); pos.Add(y);

which fixed everything (Thanks Bing)