Sampling and design of study

a) If I send a survey questionnaire by email to all members of for example the Association of Psychologists in a country, what sampling technique did I use? I would say cohort sampling, but I am not fully certain, convenience sampling seems wrong. About 20 % of them responded, and then these responses were used as the sample without follow up on non-respondents.

b) When comparing the responses of psychologists in the questionnaire to a) the general population and b) another job category like judges, am I right to say that it is an observational cohort study? I can't see how that can be experimental.

Thanks in advance!!