“…Note that various spectral problems for the Stark equation and similar equations were studied in the works Its et al (2016), Khanmamedov et al (2020), Gafarova et al (2021), Korotyaev (2017, Savchuk et al (2017), Makhmudova et al (2020), Toloza et al (2023), Gasimov, (20082013).…”