diff --git a/src/scgenerator/const.py b/src/scgenerator/const.py
index 0770e66..dcc40c5 100644
--- a/src/scgenerator/const.py
+++ b/src/scgenerator/const.py
@@ -1,5 +1,5 @@
 import numpy as np
-
+from collections import namedtuple
 
 __version__ = "0.1.0"
 
@@ -232,6 +232,7 @@ valid_variable = dict(
         "he_mode",
         "fit_parameters",
         "input_transmission",
+        "n2",
     ],
     gas=["pressure", "temperature", "gas_name", "plasma_density"],
     pulse=[
@@ -264,4 +265,4 @@ PARAM_SEPARATOR = " "
 SPEC1_FN = "spectrum_{}.npy"
 SPECN_FN = "spectra_{}.npy"
 Z_FN = "z.npy"
-PARAM_FN = "params.toml"
\ No newline at end of file
+PARAM_FN = "params.toml"