quasispontaneous

Quasispontaneous is an adjective used in some scientific literatures to describe processes that proceed with little explicit energetic input but are not strictly spontaneous in the thermodynamic sense. In this sense, "quasi" signals that an underlying driving force is present, such as a small amount of energy, a pre-existing gradient, or a source of fluctuations, which enables the transition or reaction to occur on a practical timescale.

Usage and scope: The term is informal and its meaning varies by field. It is not a formal classification in thermodynamics, and different authors may define the threshold between quasi-spontaneous and truly nonspontaneous differently. Generally, quasispontaneous processes are those that would not proceed at an appreciable rate without some ancillary factor, yet once initiated they continue with minimal ongoing input.

Mechanisms: Common features include low effective activation barriers, coupling to a reservoir (thermal, chemical, or electromagnetic), and reliance on thermal or quantum fluctuations to trigger the event. The description emphasizes that the primary impetus is near the local driving force, with the external contribution being small or transient.

Examples: In chemistry, a reaction might be described as quasispontaneous if it proceeds readily once a brief kick, such as a small amount of heat or light, is provided. In materials science and physics, phase transitions or relaxation processes may be labeled quasispontaneous when spontaneous initiation is unlikely without a seed or fluctuation, but subsequent evolution is self-sustaining.

See also: spontaneous process, activation energy, stochastic resonance, fluctuation-induced transitions.